a(n) = Sum_{k=1..n} binomial(2*n, n-k) * phi(k), where phi is the Euler totient function.

A356340

a(n) = Sum_{k=1..n} binomial(2*n, n-k) * phi(k), where phi is the Euler totient function.

Terms

    a(0) =1a(1) =5a(2) =23a(3) =102a(4) =444a(5) =1909a(6) =8133a(7) =34404a(8) =144714a(9) =605920a(10) =2527348a(11) =10507978a(12) =43569096a(13) =180219699a(14) =743907057a(15) =3065019864a(16) =12607648238a(17) =51783970314a(18) =212412697368a(19) =870249992168

External references