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A161842
Partial sums of A161841.
3
2, 4, 6, 10, 12, 16, 18, 22, 26, 30, 32, 38, 40, 44, 48, 54, 56, 62, 64, 70, 74, 78, 80, 88, 92, 96, 100, 106, 108, 116, 118, 124, 128, 132, 136, 146, 148, 152, 156, 164, 166, 174, 176, 182, 188, 192, 194, 204, 208, 214, 218, 224, 226, 234, 238, 246
OFFSET
1,1
LINKS
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