OFFSET
1,2
COMMENTS
Intersection of this sequence and A001082 is {0, 21, 1365, 87381,...} all of the form (2^(6*m)-1)/3.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).
FORMULA
a(n) = 3*(n - 1)*(3*n^2 - 3*n + 1) with n>0. Corresponding cubes are 3*a(n) + 1 = (3*n - 2)^3.
G.f.: 3*x^2*(7 + 10*x + x^2)/(1-x)^4. - Colin Barker, Apr 11 2012
MATHEMATICA
CoefficientList[Series[3 (7 + 10 x + x^2)/(1 - x)^4, {x, 0, 40}], x] (* Vincenzo Librandi, Apr 11 2012 *)
LinearRecurrence[{4, -6, 4, -1}, {0, 21, 114, 333}, 40] (* Harvey P. Dale, Mar 08 2018 *)
PROG
(Magma) [3*n*(1+3*n+3*n^2): n in [1..40]]; // Vincenzo Librandi, Apr 11 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Zak Seidov, Aug 12 2006
EXTENSIONS
0 added and b-file updated by Bruno Berselli, May 23 2017
STATUS
approved