A182481 a(n) is the least k such that 6*k*n-1 and 6*k*n+1 are twin primes, and a(n)=0, if such k does not exist.

1, 1, 1, 3, 1, 2, 1, 4, 2, 1, 3, 1, 4, 5, 2, 2, 1, 1, 2, 2, 7, 5, 1, 3, 1, 2, 5, 16, 2, 1, 7, 1, 1, 5, 2, 2, 9, 1, 8, 1, 5, 9, 4, 5, 1, 3, 1, 4, 3, 2, 7, 1, 20, 5, 2, 8, 14, 1, 3, 21, 43, 4, 6, 3, 5, 8, 4, 9, 2, 1, 3, 1, 14, 15, 9, 30, 1, 4, 22, 7, 20, 21, 9

Offset

1,4

Comments

Conjecture: a(n)>0; equivalently, for every n, the arithmetic progression {6*k*n-1} contains infinitely many lessers of twin primes (A001359).

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Mathematica

Table[k = 0; While[! (PrimeQ[6*k*n - 1] && PrimeQ[6*k*n + 1]), k++]; k, {n, 100}] (* T. D. Noe, May 02 2012 *)

Prog

(PARI) a(n)=my(k); n*=6; until(isprime(n*k++-1)&&isprime(n*k+1), ); k \\ Charles R Greathouse IV, May 01 2012

Crossrefs

Cf. A001359, A006512, A014574, A001097, A077800, A002822.

Sequence in context: A370220 A177343 A124036 * A066743 A257915 A257904

Adjacent sequences: A182478 A182479 A182480 * A182482 A182483 A182484

Keyword

nonn

Author

Vladimir Shevelev, May 01 2012

Status

approved