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A374352 a(n) = [n>1] * a(n-1) + Sum_{d|n} phi(lcm(d,n/d)) where [] is an Iverson bracket.

%I A374352 #17 Jul 05 2024 18:52:30
%S A374352 1,3,7,12,20,28,40,52,66,82,102,122,146,170,202,228,260,288,324,364,
%T A374352 412,452,496,544,588,636,684,744,800,864,924,980,1060,1124,1220,1290,
%U A374352 1362,1434,1530,1626,1706,1802,1886,1986,2098,2186,2278,2382,2472,2560,2688
%N A374352 a(n) = [n>1] * a(n-1) + Sum_{d|n} phi(lcm(d,n/d)) where [] is an Iverson bracket.
%C A374352 Sum over all positive integers k, m with k*m <= n of phi(lcm(k,m)).
%H A374352 Alois P. Heinz, <a href="/A374352/b374352.txt">Table of n, a(n) for n = 1..10000</a>
%H A374352 Wikipedia, <a href="https://en.wikipedia.org/wiki/Iverson_bracket">Iverson bracket</a>
%F A374352 a(n) = Sum_{j=1..n} Sum_{d|j} phi(lcm(d,j/d)).
%F A374352 a(n) = Sum_{j=1..n} A061884(j).
%p A374352 a:= proc(n) option remember; uses numtheory; `if`(n<1, 0,
%p A374352       a(n-1)+add(phi(ilcm(d, n/d)), d=divisors(n)))
%p A374352     end:
%p A374352 seq(a(n), n=1..66);
%Y A374352 Partial sums of A061884.
%Y A374352 Cf. A000010, A003990, A051173, A372866.
%K A374352 nonn
%O A374352 1,2
%A A374352 _Alois P. Heinz_, Jul 05 2024