A254229 Indices of centered square numbers (A001844) which are also heptagonal numbers (A000566).
1, 46, 207, 14652, 66493, 4717738, 21410379, 1519096824, 6894075385, 489144459430, 2219870863431, 157502996839476, 714791523949237, 50715475837851682, 230160650840790723, 16330225716791401968, 74111014779210663409, 5258281965330993581854
Offset: 1
Examples
46 is in the sequence because the 46th centered square number is 4141, which is also the 41st heptagonal number.
Links
- Colin Barker, Table of n, a(n) for n = 1..797
- Index entries for linear recurrences with constant coefficients, signature (1,322,-322,-1,1).
Programs
-
Mathematica
LinearRecurrence[{1,322,-322,-1,1},{1,46,207,14652,66493},20] (* Harvey P. Dale, Sep 19 2022 *) -
PARI
Vec(x*(45*x^3+161*x^2-45*x-1)/((x-1)*(x^2-18*x+1)*(x^2+18*x+1)) + O(x^100))
Formula
a(n) = a(n-1)+322*a(n-2)-322*a(n-3)-a(n-4)+a(n-5).
G.f.: x*(45*x^3+161*x^2-45*x-1) / ((x-1)*(x^2-18*x+1)*(x^2+18*x+1)).
Comments