OFFSET
1,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..3000
FORMULA
a(n) = A056045(n) for squarefree n, when all divisors are unitary.
EXAMPLE
n=100 has 9 divisors of which {1,4,25,100} are unitary, so a(100) = 100 + 3921225 + 242519269720337121015504 + 1.
MAPLE
a:= n-> add(`if`(igcd(d, n/d)=1, binomial(n, d), 0),
d=numtheory[divisors](n)):
seq(a(n), n=1..40); # Alois P. Heinz, Aug 25 2019
MATHEMATICA
a[n_] := Total[Binomial[n, Select[Divisors[n], CoprimeQ[#, n/#] &]]]; Array[a, 40] (* Amiram Eldar, Jul 28 2024 *)
PROG
(PARI) a(n) = sumdiv(n, d, if (gcd(d, n/d)==1, binomial(n, d))); \\ Michel Marcus, Aug 25 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Aug 02 2000
STATUS
approved