OFFSET
1,2
REFERENCES
H. J. S. Smith, Report on the Theory of Numbers, reprinted in Vol. 1 of his Collected Math. Papers, Chelsea, NY, 1979, see p. 322.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = Sum_{d|n} max(d, n/d). - Seiichi Manyama, Dec 27 2017
a(n) = Sum_{k in Z} H(4*n-k^2) where H() is the Hurwitz class number. - Seiichi Manyama, Jan 06 2018
G.f.: Sum_{n >= 1} x^(n^2)*(n + 2*x^n - n*x^(2*n))/(1 - x^n)^2 = x + 4*x^2 + 6*x^3 + 10*x^4 + 10*x^5 + .... Cf. A117004. - Peter Bala, Jan 19 2021
PROG
(PARI) {a(n) = sumdiv(n, d, max(d, n/d))} \\ Seiichi Manyama, Dec 27 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Apr 15 2006
STATUS
approved