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

1,1

Links

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

Example

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.

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 *)

Crossrefs

Cf. A001097, A117048, A117112.

Sequence in context: A361468 A361467 A260417 * A080563 A221520 A214311

Adjacent sequences: A117310 A117311 A117312 * A117314 A117315 A117316

Keyword

easy,nonn

Author

Greg Huber, Apr 24 2006

Extensions

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

Status

approved