A228142 Number of blocks in a Steiner system S(2, 5, A228141(n+1)).

1, 21, 30, 82, 99, 183, 208, 324, 357, 505, 546, 726, 775, 987, 1044, 1288, 1353, 1629, 1702, 2010, 2091, 2431, 2520, 2892, 2989, 3393, 3498, 3934, 4047, 4515, 4636, 5136, 5265, 5797, 5934, 6498, 6643, 7239, 7392, 8020, 8181, 8841, 9010, 9702, 9879, 10603

Offset

1,2

Links

Colin Barker, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1).

Formula

a(n) = (-3/4*(-1+(-1)^n)+(-5/2+3*(-1)^n)*n+5*n^2).

a(n) = a(n-1)+2*a(n-2)-2*a(n-3)-a(n-4)+a(n-5).

G.f.: -x*(12*x^3+7*x^2+20*x+1) / ((x-1)^3*(x+1)^2).

Prog

(PARI) Vec(-x*(12*x^3+7*x^2+20*x+1)/((x-1)^3*(x+1)^2) + O(x^100))

Crossrefs

Cf. A228141.

Sequence in context: A276655 A187965 A318349 * A276756 A115433 A116096

Adjacent sequences: A228139 A228140 A228141 * A228143 A228144 A228145

Keyword

nonn

Author

Colin Barker, Aug 12 2013

Status

approved