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%I #5 Oct 04 2020 23:31:17
%S 0,0,0,1,2,2,2,3,3,3,5,5,5,6,6,6,7,7,9,8,9,9,10,11,11,12,12,13,14,14,
%T 14,14,15,15,16,16,18,18,17,18,19,20,21,20,21,20,22,23,21,23,24,25,26,
%U 24,26,27,25,27,29,29,30,29,30,30,30,31,33,32,32,33,35,34,35,34,36,37
%N Number of ways to write n as the sum of two positive integers, s,t such that phi(s) is not equal to phi(t), where phi is the Euler totient function (A000010).
%F a(n) = Sum_{i=1..floor(n/2)} (1 - [phi(i) = phi(n-i)]), where phi is the Euler totient function (A000010) and [ ] is the Iverson bracket.
%t Table[Sum[1 - KroneckerDelta[EulerPhi[i], EulerPhi[n - i]], {i, Floor[n/2]}], {n, 100}]
%Y Cf. A000010, A337930.
%K nonn
%O 1,5
%A _Wesley Ivan Hurt_, Sep 30 2020