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A147685
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Squares and centered square numbers interleaved.
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2
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0, 1, 1, 5, 4, 13, 9, 25, 16, 41, 25, 61, 36, 85, 49, 113, 64, 145, 81, 181, 100, 221, 121, 265, 144, 313, 169, 365, 196, 421, 225, 481, 256, 545, 289, 613, 324, 685, 361, 761, 400, 841, 441, 925, 484, 1013, 529, 1105, 576, 1201, 625, 1301, 676, 1405, 729, 1513
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OFFSET
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0,4
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COMMENTS
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This could be called the inverse Motzkin transform of A109188 since the substitution x -> x/(1+x+x^2) in the independent variable of the g.f. A109188(x) yields this sequence here.
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LINKS
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FORMULA
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O.g.f.: x*(1+x+x^2)*(1+x^2)/((1-x)^3*(1+x)^3).
a(n) = 3*a(n-2) - 3*a(n-4) + a(n-6), n>5.
Euler transform of length 4 sequence [ 1, 4, -1, -1]. - Michael Somos, Aug 07 2014
a(2n+1) = a(2n) + a(2n+2) for all n in Z. - Michael Somos, Aug 07 2014
A120328(n-1) = 3*n^2 + 2 = a(2*n + 1) - a(2*n)+ a(2*n - 1) for all n in Z. - Michael Somos, Aug 07 2014
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EXAMPLE
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G.f. = x + x^2 + 5*x^3 + 4*x^4 + 13*x^5 + 9*x^6 + 25*x^7 + 16*x^8 + 41*x^9 + ...
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MAPLE
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MATHEMATICA
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CoefficientList[Series[x (1 + x + x^2) (1 + x^2)/((1 - x)^3 (1 + x)^3), {x, 0, 50}], x] (* Vincenzo Librandi, Aug 07 2014 *)
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PROG
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(PARI) {a(n) = if( n%2, (n^2 + 1) / 2, n^2 / 4)}; /* Michael Somos, Aug 07 2014 */
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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