OFFSET
1,2
COMMENTS
Also structured pentakis dodecahedral numbers (vertex structure 7) (cf. A100173 = alternate vertex).
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..5000
Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).
FORMULA
a(n) = (1/6)*(54*n^3 - 72*n^2 + 24*n) = n*(3*n-2)^2.
From Jaume Oliver Lafont, Sep 08 2009: (Start)
a(n) = (3*(n-1) + 1)^2*(3*(n-1) + 3)/3.
G.f.: x*(1 + 28*x + 25*x^2)/(1-x)^4. (End)
MATHEMATICA
Table[(3(n-1)+1)^2(3(n-1)+3)/3, {n, 40}] (* Harvey P. Dale, Jan 02 2020 *)
PROG
(Magma) [(1/6)*(54*n^3-72*n^2+24*n): n in [1..40]]; // Vincenzo Librandi, Jul 26 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
James A. Record (james.record(AT)gmail.com), Nov 07 2004
STATUS
approved