A185542 a(n) = m*(m+1)/2, where m = floor(n^(5/2)).

1, 15, 120, 528, 1540, 3916, 8385, 16471, 29646, 50086, 80601, 124251, 185745, 269011, 379756, 524800, 709836, 944625, 1237951, 1599366, 2041210, 2577585, 3216916, 3980431, 4884375, 5939181, 7172578, 8605026, 10253656, 12149985, 14313925, 16776528, 19565640, 22717170, 26263128, 30236976, 34673628

Offset: 1

Author

Clark Kimberling, Jan 30 2011

Keywords

• nonn

Comments

A subsequence of A000217, the triangular numbers.

Links

• G. C. Greubel, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A000217, A155013.

Programs

Mathematica

f[n_] = Floor[n^(5/2)]*Floor[n^(5/2)+1]/2; Table[f[n],{n,1,80}]
(#(#+1))/2&/@Floor[Range[40]^(5/2)] (* Harvey P. Dale, Feb 27 2024 *)

PARI

for(n=1,50, print1(floor(n^(5/2))*floor(1 + n^(5/2))/2, ", ")) \\ G. C. Greubel, Jul 07 2017

Formula

a(n) = A000217(A155013(n)). - Michel Marcus, Jul 08 2017