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A253675
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Centered triangular numbers (A005448) which are also centered octagonal numbers (A016754).
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3
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1, 361, 6241, 3463321, 59923081, 33254804881, 575381414521, 319312633001041, 5524812282304561, 3066039868821187801, 53049246959306977201, 29440114501108412261161, 509378863778453312776441, 282683976373603105710477121, 4891055796951461749972406281
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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+360*x^3-3722*x^2+360*x+1) / ((x-1)*(x^2-98*x+1)*(x^2+98*x+1)).
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EXAMPLE
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361 is in the sequence because it is the 16th centered triangular number and the 10th centered octagonal number.
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MATHEMATICA
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LinearRecurrence[{1, 9602, -9602, -1, 1}, {1, 361, 6241, 3463321, 59923081}, 20] (* Harvey P. Dale, Dec 09 2017 *)
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PROG
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(PARI) Vec(-x*(x^4+360*x^3-3722*x^2+360*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. A005448, A016754, A253673, A253674.
Sequence in context: A231975 A112078 A303257 * A206249 A231996 A302385
Adjacent sequences: A253672 A253673 A253674 * A253676 A253677 A253678
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KEYWORD
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nonn,easy
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AUTHOR
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Colin Barker, Jan 08 2015
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STATUS
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approved
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