OFFSET
1,2
LINKS
Scott R. Shannon, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = Sum_{k=1 .. 1+floor(log_2(n))} Sum_{p=2..floor(n^(1/(k-1)))} phi(p)*floor(n/p^(k-1)) where phi is the Euler phi-function A000010.
EXAMPLE
For n = 6, the a(6) = 22 GPs are: all 6 singletons, all 15 pairs, and one triple 1,2,4.
MAPLE
CROSSREFS
KEYWORD
nonn
AUTHOR
Scott R. Shannon and N. J. A. Sloane, Oct 23 2023
STATUS
approved