A078503 - OEIS

%I #5 May 06 2020 21:03:48

%S 1,2,1,6,0,15,0,15,0,210,0,495,0,28,1,12870,0,18564,0,495,0,646646,0,

%T 125970,0,18564,0,30421755,0,5852925,0,4845,0,735471,0,1251677700,0,

%U 134596,0,62852101650,0,11058116888,0,10626,0,7890371113950,0

%N a(n) = binomial(phi(n+1),phi(n)).

%t Table[Binomial[EulerPhi[i + 1], EulerPhi[i]], {i, 1, 50}]

%Y Cf. A000010.

%K nonn

%O 1,2

%A _Joseph L. Pe_, Jan 05 2003