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a(n) = Sum_{d|n} (Stirling2(n,d) mod 2).
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%I #6 Nov 02 2021 08:33:26

%S 1,2,2,3,2,3,2,4,3,4,2,4,2,3,3,5,2,5,2,5,3,3,2,5,3,3,4,4,2,5,2,6,3,4,

%T 3,7,2,3,3,6,2,5,2,4,4,3,2,6,2,5,4,4,2,5,2,5,4,3,2,6,2,3,4,7,3,5,2,6,

%U 3,5,2,8,2,4,4,4,3,5,2,7,4,4,2,6,4,3,3,5,2,7,3,4,3,3,2,7,2,3,6,6

%N a(n) = Sum_{d|n} (Stirling2(n,d) mod 2).

%t Table[DivisorSum[n, Mod[StirlingS2[n, #], 2] &], {n, 1, 100}]

%o (PARI) a(n) = sumdiv(n, d, stirling(n, d, 2) % 2); \\ _Michel Marcus_, Nov 02 2021

%Y Cf. A007306, A008277, A246600, A308037.

%K nonn

%O 1,2

%A _Ilya Gutkovskiy_, Nov 02 2021