OFFSET
1,1
REFERENCES
Steven R. Finch, Mathematical Constants II, Encyclopedia of Mathematics and Its Applications, Cambridge University Press, Cambridge, 2018, p. 162.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..5000
Yoichi Motohashi, An asymptotic formula in the theory of numbers, Acta Arith. 16 (1969/70), 255-264. MR0266884 (42 #1786).
J. Sandor, D. S. Mitrinovic, B. Crstici, Handbook of Number Theory I, Volume 1, Springer, 2005, p. 63.
FORMULA
a(n) ~ (c/Pi^2) * n * log(n)^4, where c = Product_{p prime} (1 - 1/p + (1/p)*(1 - 1/p)^2*(1 + 1/p)^(-1)) = 0.358231... - Amiram Eldar, Mar 08 2020
MATHEMATICA
Accumulate[a[n_]:=DivisorSum[n+1, DivisorSigma[0, n]^2 &]; Array[a, 56]] (* Vincenzo Librandi, Jan 12 2020 *)
PROG
(Magma) [&+[#Divisors(i)^2*#Divisors(i+1):i in [1..n]]:n in [1..60]]; // Marius A. Burtea, Jan 12 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jan 11 2020
STATUS
approved