A024401 a(n) = [ (3rd elementary symmetric function of S(n))/(2nd elementary symmetric function of S(n)) ], where S(n) = {first n+2 positive integers congruent to 2 mod 3}.

1, 3, 6, 11, 16, 22, 30, 38, 47, 58, 69, 81, 95, 109, 124, 141, 158, 176, 196, 216, 237, 260, 283, 307, 333, 359, 386, 415, 444, 474, 506, 538, 571, 606, 641, 677, 715, 753, 792, 833, 874, 916, 960

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Crossrefs

Cf. A024391, A024392.

Formula

Conjecture: a(n) = 2*a(n-1) - a(n-2) + a(n-3) - 2*a(n-4) + a(n-5). G.f. x*(-1-x-x^3-x^2+x^4) / ( (1+x+x^2)*(x-1)^3 ). - R. J. Mathar, Oct 08 2011

a(n) = floor(A024392(n) / A024391(n+1)). - Sean A. Irvine, Jul 07 2019