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 A253675 Centered triangular numbers (A005448) which are also centered octagonal numbers (A016754). 3
 1, 361, 6241, 3463321, 59923081, 33254804881, 575381414521, 319312633001041, 5524812282304561, 3066039868821187801, 53049246959306977201, 29440114501108412261161, 509378863778453312776441, 282683976373603105710477121, 4891055796951461749972406281 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS 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). FORMULA 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)). EXAMPLE 361 is in the sequence because it is the 16th centered triangular number and the 10th centered octagonal number. MATHEMATICA LinearRecurrence[{1, 9602, -9602, -1, 1}, {1, 361, 6241, 3463321, 59923081}, 20] (* Harvey P. Dale, Dec 09 2017 *) PROG (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)) CROSSREFS Cf. A005448, A016754, A253673, A253674. Sequence in context: A231975 A112078 A303257 * A206249 A231996 A302385 Adjacent sequences:  A253672 A253673 A253674 * A253676 A253677 A253678 KEYWORD nonn,easy AUTHOR Colin Barker, Jan 08 2015 STATUS approved

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Last modified January 16 09:13 EST 2021. Contains 340204 sequences. (Running on oeis4.)