A087383 Primes p such that p is a twin prime and prime(prime(p)) is also a twin prime.

3, 5, 7, 13, 29, 41, 43, 59, 71, 103, 107, 137, 149, 193, 199, 271, 281, 311, 347, 349, 433, 463, 569, 617, 619, 811, 827, 857, 859, 881, 1031, 1153, 1229, 1289, 1481, 1607, 1699, 1723, 1933, 1949, 1951, 1997, 2113, 2551, 2593, 2657, 3001, 3257, 3373, 3463

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

29 is in the sequence because 29 and 31 are twin primes and prime(prime(29)) = prime(109) = 599, which is a twin prime with 601.

Mathematica

TwinPrimeQ[n_]:=If[PrimeQ[n], If[PrimeQ[n-2]||PrimeQ[n+2], True, False], False](*TwinPrimeQ*) lst={}; Do[If[TwinPrimeQ[Prime[Prime[n]]]&&TwinPrimeQ[n], AppendTo[lst, n]], {n, 7!}]; lst (* Vladimir Joseph Stephan Orlovsky, Sep 07 2008 *)

Prog

(PARI) twips(n) = { c1=0; c2=0; forprime(x=3, n, if(isprime(x+2), c1++); x1=prime(prime(x)); if(isprime(x-2) || isprime(x+2), if(isprime(x1-2) || isprime(x1+2), print1(x", "); c2++; ) ) ); print(); print(c2/c1+.0) }

Crossrefs

Cf. A001097, A006450.

Sequence in context: A224222 A224221 A128547 * A038928 A359436 A225504

Adjacent sequences: A087380 A087381 A087382 * A087384 A087385 A087386

Keyword

easy,nonn

Author

Cino Hilliard, Oct 21 2003

Status

approved