A181414 Products of exactly two Pillai primes.

529, 667, 841, 1357, 1403, 1541, 1633, 1711, 1769, 1817, 1909, 1943, 2059, 2291, 2407, 2507, 3161, 3481, 3599, 3721, 3953, 4087, 4189, 4331, 4489, 4661, 4757, 4819, 4897, 5041, 5063, 5293, 5561, 5609, 5893, 6241, 6431, 6557, 6649, 6889

Offset

1,1

Comments

It would not be right to call these "Pillai semiprimes" as that would better describe semiprimes k such that there exists an integer m such that m!+1 is 0 mod k and k is not 1 mod m.

There are no pairs (n, n+1) in this sequence since all terms are odd. The first few n such that n and n+2 are in the sequence are 11771, 14099, 19337, 32729, 32741, 34829, 37391, 38249, 39467, 40319, 41747, ... - Charles R Greathouse IV, Jan 28 2011

Links

Table of n, a(n) for n=1..40.

Formula

{A063980(i) * A063980(j)}.

Example

a(2) = 23*29.

Crossrefs

Cf. A001358, A063980.

Sequence in context: A205309 A045788 A339636 * A020289 A274932 A082409

Adjacent sequences: A181411 A181412 A181413 * A181415 A181416 A181417

Keyword

nonn,easy

Author

Jonathan Vos Post, Jan 28 2011

Status

approved