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A063249 Doubly hexagonal numbers. 7
0, 1, 66, 435, 1540, 4005, 8646, 16471, 28680, 46665, 72010, 106491, 152076, 210925, 285390, 378015, 491536, 628881, 793170, 987715, 1216020, 1481781, 1788886, 2141415, 2543640, 3000025, 3515226, 4094091, 4741660, 5463165 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
LINKS
FORMULA
a(n) = n*(2*n-1)(4*n^2-2*n-1) = A000384(A000384(n)).
G.f.: -x*(15*x^3+115*x^2+61*x+1) / (x-1)^5. - Colin Barker, Sep 14 2014
EXAMPLE
a(2)=66 since 6 is the 2nd hexagonal number and 66 is the 6th hexagonal number.
MATHEMATICA
LinearRecurrence[{5, -10, 10, -5, 1}, {0, 1, 66, 435, 1540}, 30] (* Harvey P. Dale, Dec 02 2016 *)
PROG
(PARI) concat(0, Vec(-x*(15*x^3+115*x^2+61*x+1)/(x-1)^5 + O(x^100))) \\ Colin Barker, Sep 14 2014
CROSSREFS
Cf. A002817 for doubly triangular numbers, A000583 for doubly square numbers and A232713 for doubly pentagonal numbers.
Sequence in context: A244286 A223444 A084027 * A106212 A155022 A202639
KEYWORD
nonn,easy
AUTHOR
Henry Bottomley, Jul 11 2001
STATUS
approved

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Last modified July 17 14:36 EDT 2024. Contains 374377 sequences. (Running on oeis4.)