OFFSET
1,2
COMMENTS
Sum over all positive integers k, m with k*m <= n of phi(lcm(k,m)).
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000
Wikipedia, Iverson bracket
FORMULA
a(n) = Sum_{j=1..n} Sum_{d|j} phi(lcm(d,j/d)).
a(n) = Sum_{j=1..n} A061884(j).
MAPLE
a:= proc(n) option remember; uses numtheory; `if`(n<1, 0,
a(n-1)+add(phi(ilcm(d, n/d)), d=divisors(n)))
end:
seq(a(n), n=1..66);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jul 05 2024
STATUS
approved