OFFSET
0,1
COMMENTS
a(n) is nearly 2*10^(2*n) because a(n) is almost (4*10^n+3)^2 / 8.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..17
FORMULA
a(n) = A008440(10^n).
a(n) = 1/8 * (Sum_{d|4*10^n+3, d == 3 mod 4} d^2 - Sum_{d|4*10^n+3, d == 1 mod 4} d^2).
EXAMPLE
a(0) = 1/8 * (Sum_{d|7, d == 3 mod 4} d^2 - Sum_{d|7, d == 1 mod 4} d^2) = 1/8 * (7^2 - 1^2) = 6.
a(1) = 1/8 * (Sum_{d|43, d == 3 mod 4} d^2 - Sum_{d|43, d == 1 mod 4} d^2) = 1/8 * (43^2 - 1^2) = 231.
a(2) = 1/8 * (Sum_{d|403, d == 3 mod 4} d^2 - Sum_{d|403, d == 1 mod 4} d^2) = 1/8 * (403^2 + 31^2 - 13^2 - 1^2) = 20400.
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, May 06 2017
EXTENSIONS
More terms from Seiichi Manyama, May 07 2017
STATUS
approved