login
A259159
Positive squares (A000290) that are heptagonal numbers (A000566) divided by 2.
3
9, 938961, 97353360225, 10093791093915321, 1046544448101974957529, 108507821458015176452612289, 11250307943363385076857772396401, 1166454428075294670080752381151042025, 120940328000452394039949183305644566845481
OFFSET
1,1
FORMULA
G.f.: -9*x*(x^2+646*x+1) / ((x-1)*(x^2-103682*x+1)).
EXAMPLE
9 is in the sequence because 9 is the 3rd square, and 2*9 is the 3rd heptagonal number.
MATHEMATICA
LinearRecurrence[{103683, -103683, 1}, {9, 938961, 97353360225}, 20] (* Vincenzo Librandi, Jun 20 2015 *)
PROG
(PARI) Vec(-9*x*(x^2+646*x+1)/((x-1)*(x^2-103682*x+1)) + O(x^20))
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Jun 19 2015
STATUS
approved