A139117 Triangular numbers (A000217) with indices A000043.

3, 6, 15, 28, 91, 153, 190, 496, 1891, 4005, 5778, 8128, 135981, 184528, 818560, 2427706, 2602621, 5176153, 9046131, 9783676, 46943205, 49416711, 62871291, 198751953, 235477551, 269340445, 990013753, 3718970646, 6105511756, 8718535225, 23347768186, 286403014380

Offset: 1

Author

Omar E. Pol, May 08 2008

Keywords

• nonn

Examples

			a(4) = 28 because A000043(4) = 7 and the 7th triangular number A000217(7) is 28.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..48

Crossrefs

Cf. A000217, A000396, A034953.

Programs

Mathematica

Map[#*(#+1)/2 &, MersennePrimeExponent[Range[48]]] (* Amiram Eldar, Oct 21 2024 *)

Formula

a(n) = A000217(A000043(n)).