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 A161999 For n even a(n) = a(n-1) + 10*a(n-2), for n odd a(n) = a(n-3) + 10 a(n-2); with a(1) = 0, a(2) = 1. 2
 0, 1, 1, 10, 20, 101, 301, 1030, 4040, 10601, 51001, 110050, 620060, 1151501, 7352101, 12135070, 85656080, 128702801, 985263601, 1372684090, 11225320100, 14712104501, 126965305501, 158346365110, 1427999420120 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 Index entries for linear recurrences with constant coefficients, signature (0, 20, 0, -99). FORMULA a(n)=20*a(n-2)-99*a(n-4). G.f.: -x^2*(-1-x+10*x^2)/((3*x-1)*(3*x+1)*(11*x^2-1)). [From R. J. Mathar, Jul 13 2009] EXAMPLE As pairs: 0, 1 1, 10 20, 101 301, 1030 4040, 10601 51001, 110050 620060, 1151501 7352101, 12135070 85656080, 128702801 MATHEMATICA nxt[{n_, a_, b_, c_}]:={n+1, b, c, If[OddQ[n], c+10b, a+10b]}; NestList[nxt, {2, 0, 1, 1}, 30][[All, 2]] (* or *) LinearRecurrence[{0, 20, 0, -99}, {0, 1, 1, 10}, 30] (* Harvey P. Dale, May 03 2018 *) CROSSREFS Combination of A081192 and A016190. Triangle A007318 (even /uneven rows). Partly same function as A015446. A001020 (as sum of pairs of 2n).A001019 (as difference of pairs of 2n) Cf. A162849. Sequence in context: A166641 A101244 A260743 * A086069 A220012 A154330 Adjacent sequences:  A161996 A161997 A161998 * A162000 A162001 A162002 KEYWORD nonn,less AUTHOR Mark Dols, Jun 24 2009, Jun 28 2009, Jul 13 2009 EXTENSIONS Edited by N. J. A. Sloane, Jun 30 2009 NAME adapted to offset. - R. J. Mathar, Jun 19 2021 STATUS approved

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Last modified December 2 08:31 EST 2021. Contains 349437 sequences. (Running on oeis4.)