OFFSET
1,3
COMMENTS
Solving the Diophantine equation A051870(m) = m*(8*m-7) = k^2 leads to the entries.
k in the sequence and a list of associated m = 0, 1, 4, 16, 121, 529, 4096, 17956, 139129, 609961...
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (0,34,0,-1).
FORMULA
a(n) = 34*a(n-2) - a(n-4), n>5. - R. J. Mathar, Oct 04 2009
G.f.: x^2*(x+1)*(x^2 + 9*x + 1)/((x^2 - 6*x + 1)*(x^2 + 6*x + 1)). - Colin Barker, Oct 07 2012
MATHEMATICA
Join[{0}, LinearRecurrence[{0, 34, 0, -1}, {1, 10, 44, 340}, 23]] (* Ray Chandler, Aug 01 2015 *)
PROG
(PARI) is(n)=ispolygonal(n^2, 18) \\ Charles R Greathouse IV, Feb 14 2013
(PARI) concat(0, Vec(x^2*(x+1)*(x^2+9*x+1)/((x^2-6*x+1)*(x^2+6*x+1)) + O(x^50))) \\ Colin Barker, Jun 24 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Sture Sjöstedt, Jun 01 2009, Jul 02 2009
EXTENSIONS
0 added in front and extended by R. J. Mathar, Oct 04 2009
STATUS
approved