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%I #6 May 07 2021 09:20:16
%S 0,0,1,1,2,1,2,2,2,2,2,2,4,2,3,3,3,2,3,3,4,2,2,3,4,4,3,4,3,3,4,3,4,3,
%T 5,4,6,3,5,3,4,4,3,4,5,2,2,3,3,4,4,5,3,3,4,5,6,3,2,3,7,4,6,4,6,4,4,4,
%U 4,5,3,5,7,6,4,6,7,5,3,4,4,4,2,5,4,3,4
%N a(n) is the number of primes p such that (p-1)|A000010(n).
%C Conjecture: a(n) > 0 for n > 2.
%e For n = 13: A000010(13) = 12 and for p = 2, 3, 5, 7 we have p-1 = 1, 2, 4, 6 and 12 is divisible by each value of p-1, so a(13) = 4.
%o (PARI) a(n) = my(e=eulerphi(n), i=0); forprime(p=2, e, if(e%(p-1)==0, i++)); i
%Y Cf. A000010, A343902, A343903.
%K nonn
%O 1,5
%A _Felix Fröhlich_, May 03 2021