A356343 a(n) = Sum_{k=1..n} binomial(2*n, k) * phi(k), where phi is the Euler totient function.
2, 10, 61, 288, 1723, 6524, 37441, 158504, 737019, 2867500, 15200293, 56951428, 291648771, 1141099348, 4686310739, 19016248192, 95307214595, 358297247772, 1748879020425, 6725041736572, 27649247188159, 108460437728204, 522912325647543, 1966622896068784, 8831400010510925
Offset: 1
Keywords
Programs
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Mathematica
Table[Sum[Binomial[2*n, k]*EulerPhi[k], {k, 1, n}], {n, 1, 30}] -
PARI
a(n) = sum(k=1, n, binomial(2*n, k) * eulerphi(k)); \\ Michel Marcus, Aug 05 2022
Formula
a(n) ~ 3 * n * 4^n / Pi^2.