OFFSET
1,1
LINKS
Colin Barker, Table of n, a(n) for n = 1..400
Index entries for linear recurrences with constant coefficients, signature (195,-195,1).
FORMULA
a(n) = 195*a(n-1) - 195*a(n-2) + a(n-3) for n>3.
G.f.: 63*x / ((1 - x)*(1 - 194*x + x^2)).
EXAMPLE
63 is in the sequence because 3*63+1 = 190 and 4*63+1 = 253 are both triangular numbers.
PROG
(PARI) Vec(63*x / ((1 - x)*(1 - 194*x + x^2)) + O(x^20))
(PARI) isok(k) = ispolygonal(3*k+1, 3) & ispolygonal(4*k+1, 3)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Dec 04 2016
STATUS
approved