A088486 Primes p of the form k*(k + 1) - 1 such that p and p + 2 are twin primes.

5, 11, 29, 41, 71, 239, 419, 461, 599, 1481, 1721, 2549, 2969, 3539, 4421, 8009, 10301, 17291, 19181, 20021, 23561, 24179, 27059, 31151, 35531, 41411, 42641, 43889, 46439, 47741, 53591, 55931, 60761, 83231, 84389, 95789, 98909, 123551, 143261, 156419, 164429

Offset: 1

Author

Pierre CAMI, Nov 09 2003

Keywords

• nonn

Comments

a(n) + 1 is an oblong number (A002378). - Michel Marcus, Feb 04 2017

Examples

			20*20 + 20 - 1 = 419, 419 and 421 twin primes, 419 is the 7th of the sequence for k = 20.
		

Links

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

Crossrefs

Cf. A002378, A088485.

Programs

Mathematica

Select[Table[k(k+1)-1,{k,500}],AllTrue[#+{0,2},PrimeQ]&] (* Harvey P. Dale, Jul 08 2024 *)

Formula

a(n) = A088485(n)*(A088485(n) + 1) - 1. - R. J. Mathar, Nov 14 2009

Extensions

Sign in definition corrected by R. J. Mathar, Nov 13 2009