A129752 Triangular numbers t which are average of two consecutive primes p and p+4.

15, 21, 45, 105, 231, 351, 465, 741, 861, 1431, 1485, 3081, 3321, 4005, 7875, 10731, 11175, 11781, 13695, 14535, 17205, 17391, 18915, 21321, 22155, 23871, 30135, 33411, 36585, 39621, 42195, 51681, 58311, 80601, 90525, 92235, 97461, 108345

Offset: 1

Author

Zak Seidov, May 14 2007

Keywords

• nonn

Comments

All terms are multiples of 3.

Examples

			15-/+2=(13,17), 21-/+2=(19,23), 45-/+2=(43,47) are pairs of consecutive primes.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000217, A024675, A130178.

Programs

Maple

select(t -> isprime(t-2) and isprime(t+2), [seq(i*(i+1)/2,i=1..1000)]); # Robert Israel, Oct 18 2020

Formula

t-/+2 are pair of consecutive primes.