A139116 a(n) = p*(p-1)/2, where p is A000043(n).

1, 3, 10, 21, 78, 136, 171, 465, 1830, 3916, 5671, 8001, 135460, 183921, 817281, 2425503, 2600340, 5172936, 9041878, 9779253, 46933516, 49406770, 62860078, 198732016, 235455850, 269317236, 989969256, 3718884403, 6105401253, 8718403176, 23347552095, 286402257541

Offset: 1

Author

Omar E. Pol, May 10 2008

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..48 (terms 1..47 from Harvey P. Dale)

Crossrefs

Cf. A000043, A000217, A036689, A139306, A139307, A139116, A139223, A139224, A139225, A139226.

Programs

Mathematica

(#(#-1))/2&/@MersennePrimeExponent[Range[47]] (* Harvey P. Dale, Aug 13 2021 *)

Formula

a(n) = A000043(n)*(A000043(n)-1)/2.

Extensions

a(24)-a(32) from Harvey P. Dale, Aug 13 2021