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A007510
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Single (or isolated or non-twin) primes: Primes p such that neither p-2 nor p+2 is prime.
(Formerly M2130)
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98
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2, 23, 37, 47, 53, 67, 79, 83, 89, 97, 113, 127, 131, 157, 163, 167, 173, 211, 223, 233, 251, 257, 263, 277, 293, 307, 317, 331, 337, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 439, 443, 449, 457, 467, 479, 487, 491, 499, 503, 509, 541, 547, 557, 563
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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Almost all primes are a member of this sequence by Brun's theorem.
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REFERENCES
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Richard L. Francis, "Isolated Primes", J. Rec. Math., 11 (1978), 17-22.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Jens Kruse Andersen, Paul Underwood and Pierre Cami,Chen prime with 70301 digits,digest of 3 messages in primeform Yahoo group, Oct 7, 2005.
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FORMULA
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EXAMPLE
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All primes congruent to 7 mod 15 are members, except for 7. All terms ofA102723are members, except for 5. -Jonathan Sondow,Oct 27 2017
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MAPLE
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with(numtheory): for i from 1 to 150 do p:=ithprime(i): if(not isprime(p+2) and not isprime(p-2)) then printf( "%d,", p) fi od: # Pab Ter
isA007510:= proc(n) isprime(n) and not isprime(n+2) and not isprime(n-2); simplify(%); end proc:
A007510:= proc(n) if n = 1 then 2; else for a from procname(n-1)+1 do if isA007510(a) then return a; end if; end do; end if; end proc: #R. J. Mathar,Apr 26 2010
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MATHEMATICA
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Transpose[Select[Partition[Prime[Range[100]], 3, 1], #[[2]] - #[[1]]!= 2 && #[[3]] - #[[2]]!= 2 &]][[2]] (*Harvey P. Dale,Mar 01 2001 *)
Select[Prime[Range[4, 100]],!PrimeQ[ #-2]&&!PrimeQ[ #+2]&] (*Zak Seidov,May 07 2007 *)
Select[Prime[Range[150]], NoneTrue[#+{2, -2}, PrimeQ]&] (*Harvey P. Dale,Dec 26 2022 *)
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PROG
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(UBASIC) 10 'primes using counters 20 N=3:print "2";:print "3";:C=2 30 A=3:S=sqrt(N) 40 B=N\A 50 if B*A=N then 55 55 Q=N+2:R=N-2: if Q<>prmdiv(Q) and N=prmdiv(N) and R<>prmdiv(R) then print Q; N; R; "-";:stop:else N=N+2:goto 30 60 A=A+2 70 if A<=sqrt(N) then 40:stop 81 C=C+1 100 N=N+2:goto 30 'Enoch Haga,Oct 08 2007
(PARI) forprime(x=2, 1000, if(!isprime(x-2)&&!isprime(x+2), print(x))) \\Zak Seidov,Mar 23 2009
(PARI) list(lim)=my(v=List([2]), p=3, q=5); forprime(r=7, lim, if(q-p>2 && r-q>2, listput(v, q)); p=q; q=r); p=precprime(lim); if(p<=lim && p-precprime(p-2)>2 && nextprime(p+2)-p>2, listput(v, p)); Vec(v) \\Charles R Greathouse IV,Aug 21 2017
(Magma) [p: p in PrimesUpTo(1000)| not IsPrime(p-2) and not IsPrime(p+2)]; //Vincenzo Librandi,Jun 20 2014
(Haskell)
import Data.List (elemIndices)
a007510 n = a007510_list!! (n-1)
a007510_list = map (+ 1) $ elemIndices (0, 1, 0) $
zip3 (drop 2 a010051_list) a010051_list (0: 0: a010051_list)
(Python)
from sympy import nextprime
def aupto(limit):
n, p, q = 1, 2, 3
alst, non_twins, twins = [], [2], [3]
while True:
p, q = q, nextprime(q)
if q - p == 2:
if p!= twins[-1]: twins.append(p)
twins.append(q)
else:
if p!= twins[-1]: non_twins.append(p)
if q > limit: return non_twins
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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EXTENSIONS
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More terms from Pab Ter (pabrlos2(AT)yahoo ), Nov 11 2005
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STATUS
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approved
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