OFFSET
1,4
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
If p is prime, a(p^k) = A000330(1+floor(k/2)). - Robert Israel, Nov 30 2016
MAPLE
f:= proc(n) add(numtheory:-tau(d)^2, d = select(t -> (t^2<=n), numtheory:-divisors(n))) end proc:
map(f, [$1..100]); # Robert Israel, Nov 30 2016
MATHEMATICA
a[n_] := DivisorSum[n, DivisorSigma[0, #]^2 &, #^2 <= n &]; Array[a, 100] (* Amiram Eldar, Aug 29 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, (d<=sqrtn(n, 2))*numdiv(d)^2) \\ Michel Marcus, Jul 21 2013
(PARI) a(n)=my(s=sqrtint(n)); sumdiv(n, d, if(d<=s, numdiv(d)^2)) \\ Charles R Greathouse IV, Jul 22 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Jul 21 2013
STATUS
approved