A024220 a(n) = [ (3rd elementary symmetric function of S(n))/(first elementary symmetric function of S(n)) ], where S(n) = {first n+2 positive integers congruent to 1 mod 3}.

2, 19, 71, 188, 410, 784, 1367, 2226, 3435, 5078, 7249, 10049, 13589, 17990, 23380, 29897, 37689, 46911, 57728, 70315, 84854, 101537, 120566, 142150, 166508, 193869, 224469, 258554, 296380, 338210, 384317, 434984, 490501, 551168, 617295, 689199

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Formula

Conjecture: a(n) = 4*a(n-1) - 6*a(n-2) + 5*a(n-3) - 5*a(n-4) + 6*a(n-5) - 4*a(n-6) + a(n-7). G.f.: x*(-2-11*x-7*x^2-8*x^3+x^4) / ( (1+x+x^2)*(x-1)^5 ). - R. J. Mathar, Oct 08 2011

a(n) = floor(A024213(n) / A000326(n+2)). - Sean A. Irvine, Jun 25 2019