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 A181389 Absolute difference between (sum of previous terms) and (n-th-even square) with a(1) = 2. 1
 2, 2, 0, 12, 20, 28, 36, 44, 52, 60, 68, 76, 84, 92, 100, 108, 116, 124, 132, 140, 148, 156, 164, 172, 180, 188, 196, 204, 212, 220, 228, 236, 244, 252, 260, 268, 276, 284, 292, 300, 308, 316, 324, 332, 340, 348, 356, 364, 372, 380, 388, 396, 404, 412, 420 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Nathaniel Johnston, Table of n, a(n) for n = 1..10000 Index entries for linear recurrences with constant coefficients, signature (2,-1). FORMULA a(n) = 8*n - 20 for n >= 4. - Nathaniel Johnston, May 27 2011 G.f.: (-2*x*(-1 + x + x^2 - 7*x^3 + 2*x^4))/(-1 + x)^2. - Alexander R. Povolotsky, Oct 18 2010 E.g.f.: 20 + 4*exp(x)*(2*x - 5) + x*(42 + (9 - 2*x)*x)/3. - Stefano Spezia, Jan 03 2023 Sum_{n>=4} (-1)^n/a(n) = (4-Pi)/16. - Amiram Eldar, Jan 08 2023 MAPLE A181389 := proc(n) local s: s:=[2, 2, 0]: if(n<=3)then return s[n]: fi: return 8*n-20: end: seq(A181389(n), n=1..100); # Nathaniel Johnston, May 27 2011 MATHEMATICA CoefficientList[Series[(-2*x*(-1 + x + x^2 - 7*x^3 + 2*x^4))/(-1 + x)^2, {x, 0, 50}], x] (* G. C. Greubel, Feb 22 2017 *) LinearRecurrence[{2, -1}, {2, 2, 0, 12, 20}, 70] (* Harvey P. Dale, Feb 13 2022 *) PROG (PARI) my(x='x+O('x^50)); Vec((-2*x*(-1 + x + x^2 - 7*x^3 + 2*x^4))/(-1 + x)^2) \\ G. C. Greubel, Feb 22 2017 CROSSREFS Cf. A017113. Sequence in context: A117270 A244137 A354127 * A091466 A134085 A151339 Adjacent sequences: A181386 A181387 A181388 * A181390 A181391 A181392 KEYWORD easy,nonn AUTHOR Giovanni Teofilatto, Oct 17 2010 STATUS approved

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Last modified December 1 07:48 EST 2023. Contains 367468 sequences. (Running on oeis4.)