OFFSET
1,1
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000
Michael Penn, This is always even??, YouTube video, 2020.
FORMULA
a(n) = 2*A094820(n).
a(n) = Sum_{i=1..n} (1 + A008836(i))*floor(n/i)). - Enrique Pérez Herrero, Jul 10 2012
a(n) ~ (log(n) + 2*gamma - 1)*n + sqrt(n), where gamma is the Euler-Mascheroni constant A001620. - Vaclav Kotesovec, Jul 01 2021
PROG
(PARI) a(n) = sum(i=1, n, floor(n/i)) + sqrtint(n) \\ David A. Corneth, Dec 17 2020
(PARI) first(n) = {my(res = vector(n), t = 0); for(i = 1, n, t+=(numdiv(i)+issquare(i)); res[i] = t ); res } \\ David A. Corneth, Dec 17 2020
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Jun 23 2009
STATUS
approved