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A259157
Positive triangular numbers (A000217) that are hexagonal numbers (A000384) divided by 2.
3
3, 3570, 4119885, 4754343828, 5486508657735, 6331426236682470, 7306460390622912753, 8431648959352604634600, 9730115592632515125415755, 11228544962248963102125146778, 12957731156319710787337293966165, 14953210525847983999624135111807740
OFFSET
1,1
COMMENTS
Intersection of A000217 and A033991 (even hexagonal numbers divided by 2). - Michel Marcus, Jun 20 2015
FORMULA
G.f.: -3*x*(35*x+1) / ((x-1)*(x^2-1154*x+1)).
EXAMPLE
3 is in the sequence because 3 is the 2nd triangular number, and 2*3 is the 2nd hexagonal number.
MATHEMATICA
LinearRecurrence[{1155, -1155, 1}, {3, 3570, 4119885}, 20] (* Vincenzo Librandi, Jun 20 2015 *)
PROG
(PARI) Vec(-3*x*(35*x+1)/((x-1)*(x^2-1154*x+1)) + O(x^20))
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Jun 19 2015
STATUS
approved