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 A026798 Number of partitions of n in which the least part is 5. 20
 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2, 3, 3, 4, 5, 6, 7, 9, 10, 13, 15, 18, 21, 26, 30, 36, 42, 50, 58, 70, 80, 95, 110, 129, 150, 176, 202, 236, 272, 317, 364, 423, 484, 560, 643, 740, 847, 975, 1112, 1277, 1456, 1666, 1897, 2168 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,16 COMMENTS Also the number of not necessarily connected 2-regular simple graphs with girth exactly 5. - Jason Kimberley, Nov 11 2011 Such partitions of n+5 correspond to A185325 partitions (parts >= 5) of n by removing a single part of size 5. - Jason Kimberley, Nov 11 2011 LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 FORMULA G.f.: x^5 * Product_{m>=5} 1/(1-x^m). a(n+5) is given by p(n) - p(n-1) - p(n-2) + 2p(n-5) - p(n-8) - p(n-9) + p(n-10) where p(n) = A000041(n). - Shanzhen Gao, Oct 28 2010 [sign of 10 and offset of formula corrected by Jason Kimberley, Nov 11 2011] a(n) ~ exp(Pi*sqrt(2*n/3)) * Pi^4 / (6*sqrt(3)*n^3). - Vaclav Kotesovec, Jun 02 2018 MAPLE ZL := [ B, {B=Set(Set(Z, card>=5))}, unlabeled ]: 1, 0, 0, 0, 0, seq(combstruct[count](ZL, size=n), n=0..54); # Zerinvary Lajos, Mar 13 2007 1, seq(coeff(series(x^5/mul(1-x^(m+5), m=0..70), x, n+1), x, n), n = 0..65); # G. C. Greubel, Nov 03 2019 MATHEMATICA f[1, 1] = 1; f[n_, k_] := f[n, k] = If[n < 0, 0, If[k > n, 0, If[k == n, 1, f[n, k + 1] + f[n - k, k]]]]; Join[{1, 0, 0, 0, 0, 1}, Table[ f[n, 5], {n, 50}]] (* Robert G. Wilson v *) Join[{1}, Drop[CoefficientList[Series[x^5/QPochhammer[x^5, x], {x, 0, 60}], x], 1]] (* G. C. Greubel, Nov 03 2019 *) PROG (PARI) my(x='x+O('x^60)); concat([1, 0, 0, 0, 0], Vec(x^5/prod(m=0, 70, 1-x^(m+5)))) \\ G. C. Greubel, Nov 03 2019 (MAGMA) R:=PowerSeriesRing(Integers(), 60); [1, 0, 0, 0, 0] cat Coefficients(R!( x^5/(&*[1-x^(m+5): m in [0..70]]) )); // G. C. Greubel, Nov 03 2019 (Sage) def A026798_list(prec):     P. = PowerSeriesRing(ZZ, prec)     return P( x^5/product((1-x^(m+5)) for m in (0..70)) ).list() a=A026798_list(65); [1]+a[1:] # G. C. Greubel, Nov 03 2019 CROSSREFS Essentially the same as A185325. Not necessarily connected 2-regular graphs with girth at least g [partitions into parts >= g]: A026807 (triangle); chosen g: A000041 (g=1 -- multigraphs with loops allowed), A002865 (g=2 -- multigraphs with loops forbidden), A008483 (g=3), A008484 (g=4), A185325(g=5), A185326 (g=6), A185327 (g=7), A185328 (g=8), A185329 (g=9). Not necessarily connected 2-regular graphs with girth exactly g [partitions with smallest part g]: A026794 (triangle); chosen g: A002865 (g=2 -- multigraphs with at least one pair of parallel edges, but loops forbidden), A026796 (g=3), A026797 (g=4), this sequence (g=5), A026799 (g=6), A026800 (g=7), A026801 (g=8), A026802 (g=9), A026803 (g=10). - Jason Kimberley, Nov 11 2011 Sequence in context: A096749 A036821 A237980 * A185325 A125890 A067661 Adjacent sequences:  A026795 A026796 A026797 * A026799 A026800 A026801 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified November 30 05:31 EST 2020. Contains 338781 sequences. (Running on oeis4.)