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 A271391 Expansion of (1 + x + 2*x^2 + 6*x^3 + x^4 + x^5)/(1 - x^2)^3. 1
 1, 1, 5, 9, 13, 25, 25, 49, 41, 81, 61, 121, 85, 169, 113, 225, 145, 289, 181, 361, 221, 441, 265, 529, 313, 625, 365, 729, 421, 841, 481, 961, 545, 1089, 613, 1225, 685, 1369, 761, 1521, 841, 1681, 925, 1849, 1013, 2025, 1105, 2209, 1201, 2401, 1301, 2601, 1405, 2809, 1513 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Centered square numbers alternating with odd squares. LINKS Index entries for linear recurrences with constant coefficients, signature (0,3,0,-3,0,1) FORMULA G.f.: (x + 5*x^2 + 6*x^3 - 2*x^4 + x^5 + x^6)/(1 - x^2)^3 E.g.f.: ((2 + x*(2 + x))*cosh(x) + x*(3 + 2*x)*sinh(x))/2. a(n) = 3*a(n-2) -3*a(n-4) + a(n-6). a(n) = (3*n^2 + 2*n + 2 + (-1)^n*(-n^2 + 2*n + 2))/4. EXAMPLE Illustration of initial terms:                                                       o                             o       o o o o o       o o o           o     o o o     o o o     o o o o o     o o o o o o   o   o o o   o o o   o o o o o   o o o o o   o o o o o o o           o     o o o     o o o     o o o o o     o o o o o                             o       o o o o o       o o o                                                       o 0   1     2       3         4           5             6 MAPLE a:=series((1+x+2*x^2+6*x^3+x^4+x^5)/(1-x^2)^3, x=0, 55): seq(coeff(a, x, n), n=0..54); # Paolo P. Lava, Mar 27 2019 MATHEMATICA LinearRecurrence[{0, 3, 0, -3, 0, 1}, {1, 1, 5, 9, 13, 25}, 55] Table[(3 n^2 + 2 n + 2 + (-1)^n (-n^2 + 2 n + 2))/4, {n, 0, 54}] PROG (PARI) x='x+O('x^99); Vec((1+x+2*x^2+6*x^3+x^4+x^5)/(1-x^2)^3) \\ Altug Alkan, Apr 06 2016 CROSSREFS Cf. A001844, A016754. Sequence in context: A314798 A208718 A208774 * A151907 A151895 A267190 Adjacent sequences:  A271388 A271389 A271390 * A271392 A271393 A271394 KEYWORD nonn,easy AUTHOR Ilya Gutkovskiy, Apr 06 2016 STATUS approved

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Last modified January 24 13:24 EST 2020. Contains 331193 sequences. (Running on oeis4.)