The On-Line Encyclopedia of Integer Sequences (OEIS)

A235269 revision #5

A235269

floor(s*t/(s+t)), where s = n^2, t = triangular(n).

0, 1, 3, 6, 9, 13, 17, 23, 28, 35, 42, 50, 59, 68, 78, 88, 100, 111, 124, 137, 151, 166, 181, 197, 213, 231, 248, 267, 286, 306, 327, 348, 370, 392, 416, 439, 464, 489, 515, 542, 569, 597, 625, 655, 684, 715, 746, 778, 811, 844, 878, 912, 948, 983, 1020, 1057

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OFFSET

1,3

LINKS

Table of n, a(n) for n=1..56.

FORMULA

a(n) = floor(s*t/(s+t)) where s = A000290(n) = n^2, t = A000217(n) = n*(n+1)/2. a(n) = floor((n^3+n^2) / (3*n+1)).

PROG

(Python)

for n in range(1, 99):

s = n*n

t = n*(n+1)/2