A117313 Average of twin-prime pairs for pairs that are expressible as the sum of two triangular numbers.

12, 30, 138, 192, 462, 660, 822, 1092, 1722, 2028, 2082, 2712, 3360, 3540, 3918, 6132, 6762, 7590, 7878, 7950, 8220, 9462, 9858, 11352, 12108, 12378, 13692, 13998, 14448, 16140, 16230, 17292, 17418, 17580, 18912, 19470, 19542, 19992, 20550, 20748

Offset: 1

Author

Greg Huber, Apr 24 2006

Keywords

• easy
• nonn

Examples

			a(1) = 12 as witnessed by 11 = 1 + 10 and 13 = 3 + 10;
a(5) = 462 as witnessed by 461 = 55 + 406 and 463 = 28 + 435.
		

Crossrefs

Cf. A001097, A117048, A117112.

Programs

Mathematica

s = Select[Union@ Flatten@ Table[i(i + 1)/2 + j(j + 1)/2, {i, 200}, {j, 0, i}], PrimeQ@ # &]; t = Select[Range@ Length@s - 1, s[[ # ]] + 2 == s[[ # + 1]] &]; s[[t]] + 1 (* Robert G. Wilson v, Apr 27 2006 *)

Extensions

More terms from Robert G. Wilson v, Apr 27 2006