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A254857
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Octagonal numbers (A000567) that are also centered heptagonal numbers (A069099).
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3
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1, 8, 736, 5461, 496133, 3680776, 334392976, 2480837633, 225380369761, 1672080883936, 151906034826008, 1126980034935301, 102384442092359701, 759582871465509008, 69006962064215612536, 511957728387718136161, 46510590046839230489633, 345058749350450558263576
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OFFSET
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1,2
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LINKS
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FORMULA
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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)).
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EXAMPLE
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736 is in the sequence because it is the 16th octagonal number and the 15th centered heptagonal number.
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PROG
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(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))
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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