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A254857 Octagonal numbers (A000567) that are also centered heptagonal numbers (A069099). 3
1, 8, 736, 5461, 496133, 3680776, 334392976, 2480837633, 225380369761, 1672080883936, 151906034826008, 1126980034935301, 102384442092359701, 759582871465509008, 69006962064215612536, 511957728387718136161, 46510590046839230489633, 345058749350450558263576 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
FORMULA
a(n) = a(n-1)+674*a(n-2)-674*a(n-3)-a(n-4)+a(n-5).
G.f.: -x*(x^4+7*x^3+54*x^2+7*x+1) / ((x-1)*(x^2-26*x+1)*(x^2+26*x+1)).
EXAMPLE
736 is in the sequence because it is the 16th octagonal number and the 15th centered heptagonal number.
PROG
(PARI) Vec(-x*(x^4+7*x^3+54*x^2+7*x+1)/((x-1)*(x^2-26*x+1)*(x^2+26*x+1)) + O(x^100))
CROSSREFS
Sequence in context: A309377 A110039 A271741 * A058921 A240283 A181153
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Feb 08 2015
STATUS
approved

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Last modified March 28 15:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)