A374352 a(n) = [n>1] * a(n-1) + Sum_{d|n} phi(lcm(d,n/d)) where [] is an Iverson bracket.
1, 3, 7, 12, 20, 28, 40, 52, 66, 82, 102, 122, 146, 170, 202, 228, 260, 288, 324, 364, 412, 452, 496, 544, 588, 636, 684, 744, 800, 864, 924, 980, 1060, 1124, 1220, 1290, 1362, 1434, 1530, 1626, 1706, 1802, 1886, 1986, 2098, 2186, 2278, 2382, 2472, 2560, 2688
Offset: 1
Keywords
Links
- Alois P. Heinz, Table of n, a(n) for n = 1..10000
- Wikipedia, Iverson bracket
Programs
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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);
Formula
a(n) = Sum_{j=1..n} Sum_{d|j} phi(lcm(d,j/d)).
a(n) = Sum_{j=1..n} A061884(j).
Comments