A370880 - OEIS

A370880

Natural numbers repeated 3 times are taken in parts of successive lengths 1,2,3,..., and a(n) is the sum of the numbers in the part with length n.

1, 2, 6, 13, 23, 39, 61, 89, 126, 172, 227, 294, 373, 464, 570, 691, 827, 981, 1153, 1343, 1554, 1786, 2039, 2316, 2617, 2942, 3294, 3673, 4079, 4515, 4981, 5477, 6006, 6568, 7163, 7794, 8461, 9164, 9906, 10687, 11507, 12369, 13273, 14219, 15210, 16246

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Table of n, a(n) for n=1..46.

Nicolay Avilov, Scheme

Index entries for linear recurrences with constant coefficients, signature (3,-3,2,-3,3,-1).

FORMULA

a(n) = Sum_{i=A000217(n-1)+1..A000217(n)} A002264(i+2).

Let r = n mod 3, then we get

a(n) = n*(n^2+3)/6 if r = 0;

(n*(n^2+3)+2)/6 if r = 1;