OFFSET
1,1
LINKS
Colin Barker, Table of n, a(n) for n = 1..300
Index entries for linear recurrences with constant coefficients, signature (975,-975,1).
FORMULA
G.f.: x*(4+487*x-5*x^2) / ((1-x)*(1-974*x+x^2)).
a(n) = 975*a(n-1)-975*a(n-2)+a(n-3) for n>3.
a(n) = (-6-(27+2*sqrt(183))*(487+36*sqrt(183))^(-n)+(-27+2*sqrt(183))*(487+36*sqrt(183))^n)/12.
EXAMPLE
4387 is in the sequence because ((4387+1)^3-4387^3)/61 = 946729 = 973^2.
PROG
(PARI) Vec(x*(4+487*x-5*x^2)/((1-x)*(1-974*x+x^2)) + O(x^20))
(PARI) isok(x) = issquare(((x+1)^3-x^3)/61)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Jul 13 2016
STATUS
approved