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 A107882 Column 1 of triangle A107880. 4
 1, 2, 5, 19, 104, 766, 7197, 82910, 1136923, 18141867, 330940109, 6803936050, 155839142185, 3938383850350, 108934529005948, 3275059508166297, 106388204134734785, 3714826559490125850, 138796913898027894261 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS FORMULA G.f.: 1 = Sum_{k>=0} a(k)*x^k*(1-x)^(2 + k*(k+1)/2). From Benedict W. J. Irwin, Nov 26 2016: (Start) Conjecture: a(n) can be expressed with a series of nested sums, a(2) = Sum_{i=1..2} i+1, a(3) = Sum_{i=1..2}Sum_{j=1..i+1} j+2, a(4) = Sum_{i=1..2}Sum_{j=1..i+1}Sum_{k=1..j+2} k+3, a(5) = Sum_{i=1..2}Sum_{j=1..i+1}Sum_{k=1..j+2}Sum_{l=1..k+3} l+4. (End) EXAMPLE G.f. = 1 + 2*x + 5*x^2 + 19*x^3 + 104*x^4 + 766*x^5 + 7197*x^6 + 82910*x^7 + ... 1 = 1*(1-x)^2 + 2*x*(1-x)^3 + 5*x^2*(1-x)^5 + 19*x^3*(1-x)^8 + 104*x^4*(1-x)^12 + 766*x^5*(1-x)^17 +... MATHEMATICA a[ n_, k_: 2, j_: 0] := If[ n < 1, Boole[n >= 0], a[ n, k, j] = Sum[ a[ n - 1, i, j + 1], {i, k + j}]]; (* Michael Somos, Nov 26 2016 *) PROG (PARI) {a(n)=polcoeff(1-sum(k=0, n-1, a(k)*x^k*(1-x+x*O(x^n))^(2+k*(k+1)/2)), n)} CROSSREFS Cf. A107880, A107881, A107883. Sequence in context: A093502 A009311 A211207 * A328977 A224691 A192445 Adjacent sequences:  A107879 A107880 A107881 * A107883 A107884 A107885 KEYWORD nonn AUTHOR Paul D. Hanna, Jun 04 2005 STATUS approved

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Last modified November 25 08:38 EST 2020. Contains 338623 sequences. (Running on oeis4.)