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A255877
a(n) = (2n-2)^3 + (2n-2) - 1.
0
-1, 9, 67, 221, 519, 1009, 1739, 2757, 4111, 5849, 8019, 10669, 13847, 17601, 21979, 27029, 32799, 39337, 46691, 54909, 64039, 74129, 85227, 97381, 110639, 125049, 140659, 157517, 175671, 195169, 216059, 238389, 262207, 287561, 314499, 343069, 373319
OFFSET
1,2
COMMENTS
a(n)/a(n-1) tends to 1 as n becomes very large (of order 10^3 or more).
FORMULA
a(n) = (2*n-2)^3 + (2*n-2) - 1.
G.f.: x*(-1 + 13*x + 25*x^2 + 11*x^3)/(1-x)^4. - Vincenzo Librandi, Mar 17 2015
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n>4. - Vincenzo Librandi, Mar 17 2015
EXAMPLE
a(3) = (2*3-2)^3 + (2*3-2) - 1 = 67.
MATHEMATICA
Table[(2 n - 2)^3 + (2 n - 2) - 1, {n, 30}] (* Michael De Vlieger, Mar 17 2015 *)
PROG
(PARI) a(n)=8*n^3 - 24*n^2 + 26*n - 11 \\ Charles R Greathouse IV, Mar 17 2015
CROSSREFS
Sequence in context: A231199 A354532 A332456 * A197277 A238317 A105287
KEYWORD
sign,easy
AUTHOR
Arka Mal, Mar 08 2015
EXTENSIONS
More terms from Vincenzo Librandi, Mar 17 2015
STATUS
approved