A259079 Octagonal numbers (A000567) that are other octagonal numbers divided by 2.
280, 373212840, 497012764340408, 661878856450449219400, 881433339438556519000044120, 1173817118196415977287174306335208, 1563188689740940473437573487667885475320, 2081720262768492984525248323578863263574296200
Offset: 1
Examples
280 is in the sequence because 280 is the 10th octagonal number, and 2*280 is the 14th octagonal number.
Links
- Colin Barker, Table of n, a(n) for n = 1..163
- Index entries for linear recurrences with constant coefficients, signature (1331715,-1331715,1).
Programs
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Mathematica
LinearRecurrence[{1331715,-1331715,1},{280,373212840,497012764340408},20] (* Harvey P. Dale, Dec 04 2015 *) -
PARI
Vec(-8*x*(x^2+41580*x+35)/((x-1)*(x^2-1331714*x+1)) + O(x^20))
Formula
G.f.: -8*x*(x^2+41580*x+35) / ((x-1)*(x^2-1331714*x+1)).
Comments