A268139 Semiprimes of the form 3*n*2^n - 3*n - 2^(2+n) + 4.

6, 35, 341, 2159, 6160337, 27787211, 191126044583, 412745898649251217229, 162789115166027506149234835193, 51436190754860636195130229261336259

Offset

1,1

Links

Table of n, a(n) for n=1..10.

Ben Green and Terence Tao, The primes contain arbitrarily long arithmetic progressions, Annals of Mathematics, 167 (2008), pp. 481-547. arXiv:math/0404188 [math.NT], 2004-2007.

Mathematica

Select[Table[3 n 2^n - 3 n - 2^(2 + n) + 4, {n, 250}], PrimeOmega[#] == 2 &]

Prog

(Magma) IsSemiprime:= func<n | &+[d[2]: d in Factorization(n)] eq 2>; [s: n in [2..240] | IsSemiprime(s) where s is 3*n*2^n-3*n-2^(2+n)+4];

Crossrefs

Cf. A000043, A001348, A228121, A247147.

Sequence in context: A261080 A356494 A291595 * A361241 A051337 A267224

Adjacent sequences: A268136 A268137 A268138 * A268140 A268141 A268142

Keyword

nonn

Author

Vincenzo Librandi, Jan 27 2016

Status

approved