cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A063249 Doubly hexagonal numbers.

Original entry on oeis.org

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
Offset: 0

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Author

Henry Bottomley, Jul 11 2001

Keywords

Examples

			a(2)=66 since 6 is the 2nd hexagonal number and 66 is the 6th hexagonal number.
		

Crossrefs

Cf. A002817 for doubly triangular numbers, A000583 for doubly square numbers and A232713 for doubly pentagonal numbers.

Programs

  • Mathematica
    LinearRecurrence[{5,-10,10,-5,1},{0,1,66,435,1540},30] (* Harvey P. Dale, Dec 02 2016 *)
  • 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

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