A049638 a(n) = T(n,4), array T as in A049627.

2, 7, 9, 12, 14, 18, 19, 23, 25, 28, 30, 34, 35, 39, 41, 44, 46, 50, 51, 55, 57, 60, 62, 66, 67, 71, 73, 76, 78, 82, 83, 87, 89, 92, 94, 98, 99, 103, 105, 108, 110, 114, 115, 119, 121, 124, 126, 130, 131, 135, 137, 140, 142, 146, 147, 151, 153, 156, 158, 162

Offset: 0

Author

Clark Kimberling

Keywords

• nonn

Crossrefs

Cf. A049627.

Programs

PARI

T(n,k) = (n+1)*(k+1) - sum(i=0, n, sum(j=0, k, gcd(i,j)>1)); \\ A049627
a(n) = T(n, 4); \\ Michel Marcus, Aug 06 2021

Formula

Conjectured g.f.: 2 -x*(-7-9*x-5*x^2+2*x^3+3*x^4) / ( (1+x)*(1+x+x^2)*(x-1)^2 ). - R. J. Mathar, Oct 26 2015

Extensions

More terms from Sean A. Irvine, Aug 06 2021