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A254896
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Octagonal numbers (A000567) that are also centered square numbers (A001844).
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3
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1, 481, 8321, 4617761, 79897441, 44339739841, 767175219361, 425750177334721, 7366416376406081, 4088053158428250401, 70732329279075969601, 39253486001477883014881, 679171818371271083701921, 376911968498137474280636161, 6521407729268615666629875041
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OFFSET
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1,2
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LINKS
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Colin Barker, Table of n, a(n) for n = 1..503
Index entries for linear recurrences with constant coefficients, signature (1,9602,-9602,-1,1).
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FORMULA
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a(n) = a(n-1)+9602*a(n-2)-9602*a(n-3)-a(n-4)+a(n-5).
G.f.: -x*(x^4+480*x^3-1762*x^2+480*x+1) / ((x-1)*(x^2-98*x+1)*(x^2+98*x+1)).
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EXAMPLE
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481 is in the sequence because it is the 13th octagonal number and the 16th centered square number.
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MATHEMATICA
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LinearRecurrence[{1, 9602, -9602, -1, 1}, {1, 481, 8321, 4617761, 79897441}, 30] (* Harvey P. Dale, Feb 04 2017 *)
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PROG
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(PARI) Vec(-x*(x^4+480*x^3-1762*x^2+480*x+1)/((x-1)*(x^2-98*x+1)*(x^2+98*x+1)) + O(x^100))
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CROSSREFS
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Cf. A000567, A001844, A253673, A254895.
Sequence in context: A051980 A020271 A290338 * A165384 A165376 A214170
Adjacent sequences: A254893 A254894 A254895 * A254897 A254898 A254899
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KEYWORD
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nonn,easy
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AUTHOR
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Colin Barker, Feb 10 2015
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STATUS
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approved
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