OFFSET
1,1
COMMENTS
Partial sums of A168010.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..10000
EXAMPLE
a(2)=20 because the numbers < (2+1)^2 are 1,2,3,4,5,6,7 and 8. Then a(2) = d(1)+d(2)+d(3)+d(4)+d(5)+d(6)+d(7)+d(8) = 1+2+2+3+2+4+2+4 = 20, where d(n) is the number of divisor of n (see A000005).
MATHEMATICA
f[n_] := Plus @@ DivisorSigma[0, Range[(n + 1)^2 - 1]]; Array[f, 43] (* Robert G. Wilson v, Dec 10 2009 *)
PROG
(Python)
def A168011(n):
m = n*(n+2)
return (sum(m//k for k in range(1, n+1))<<1)-n**2 # Chai Wah Wu, Oct 23 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Nov 16 2009
EXTENSIONS
More terms from Robert G. Wilson v, Dec 10 2009
STATUS
approved