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%I #19 Feb 28 2020 04:28:57
%S 0,0,0,0,0,1,1,2,3,4,5,7,8,11,14,18,22,28,33,40,47,56,65,77,89,104,
%T 119,137,155,177,199,225,252,283,315,352,389,432,476,525,576,633,691,
%U 756,823,897,973,1057,1143,1237,1334,1439,1547,1665,1786,1917,2052
%N Number of odd parts appearing among the fourth largest parts of the partitions of n into 5 parts.
%H <a href="/index/Par#part">Index entries for sequences related to partitions</a>
%H <a href="/index/Rec#order_23">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,1,-2,1,0,0,1,-2,2,-3,3,-2,2,-1,0,0,-1,2,-1,1,-2,1).
%F a(n) = Sum_{l=1..floor(n/5)} Sum_{k=l..floor((n-l)/4)} Sum_{j=k..floor((n-k-l)/3)} Sum_{i=j..floor((n-j-k-l)/2)} (k mod 2).
%F Conjectures from _Colin Barker_, Aug 22 2019: (Start)
%F G.f.: x^5*(1 - x + x^2)*(1 - x^3 + x^6) / ((1 - x)^5*(1 + x)^2*(1 + x^2)*(1 + x + x^2)*(1 - x + x^2 - x^3 + x^4)*(1 + x^4)*(1 + x + x^2 + x^3 + x^4)).
%F a(n) = 2*a(n-1) - a(n-2) + a(n-3) - 2*a(n-4) + a(n-5) + a(n-8) - 2*a(n-9) + 2*a(n-10) - 3*a(n-11) + 3*a(n-12) - 2*a(n-13) + 2*a(n-14) - a(n-15) - a(n-18) + 2*a(n-19) - a(n-20) + a(n-21) - 2*a(n-22) + a(n-23) for n>22.
%F (End) [Conjectures verified by _Wesley Ivan Hurt_, Aug 24 2019]
%e Figure 1: The partitions of n into 5 parts for n = 10, 11, ..
%e 1+1+1+1+10
%e 1+1+1+2+9
%e 1+1+1+3+8
%e 1+1+1+4+7
%e 1+1+1+5+6
%e 1+1+1+1+9 1+1+2+2+8
%e 1+1+1+2+8 1+1+2+3+7
%e 1+1+1+3+7 1+1+2+4+6
%e 1+1+1+4+6 1+1+2+5+5
%e 1+1+1+5+5 1+1+3+3+6
%e 1+1+1+1+8 1+1+2+2+7 1+1+3+4+5
%e 1+1+1+2+7 1+1+2+3+6 1+1+4+4+4
%e 1+1+1+3+6 1+1+2+4+5 1+2+2+2+7
%e 1+1+1+1+7 1+1+1+4+5 1+1+3+3+5 1+2+2+3+6
%e 1+1+1+2+6 1+1+2+2+6 1+1+3+4+4 1+2+2+4+5
%e 1+1+1+3+5 1+1+2+3+5 1+2+2+2+6 1+2+3+3+5
%e 1+1+1+1+6 1+1+1+4+4 1+1+2+4+4 1+2+2+3+5 1+2+3+4+4
%e 1+1+1+2+5 1+1+2+2+5 1+1+3+3+4 1+2+2+4+4 1+3+3+3+4
%e 1+1+1+3+4 1+1+2+3+4 1+2+2+2+5 1+2+3+3+4 2+2+2+2+6
%e 1+1+2+2+4 1+1+3+3+3 1+2+2+3+4 1+3+3+3+3 2+2+2+3+5
%e 1+1+2+3+3 1+2+2+2+4 1+2+3+3+3 2+2+2+2+5 2+2+2+4+4
%e 1+2+2+2+3 1+2+2+3+3 2+2+2+2+4 2+2+2+3+4 2+2+3+3+4
%e 2+2+2+2+2 2+2+2+2+3 2+2+2+3+3 2+2+3+3+3 2+3+3+3+3
%e --------------------------------------------------------------------------
%e n | 10 11 12 13 14 ...
%e --------------------------------------------------------------------------
%e a(n) | 5 7 8 11 14 ...
%e --------------------------------------------------------------------------
%t LinearRecurrence[{2, -1, 1, -2, 1, 0, 0, 1, -2, 2, -3, 3, -2, 2, -1,
%t 0, 0, -1, 2, -1, 1, -2, 1}, {0, 0, 0, 0, 0, 1, 1, 2, 3, 4, 5, 7, 8,
%t 11, 14, 18, 22, 28, 33, 40, 47, 56, 65}, 50]
%o (PARI) Vec(x^5*(1-x+x^2)*(1-x^3+x^6)/((1-x)^5*(1+x)^2*(1+x^2)*(1+x+x^2)*(1-x+x^2-x^3+x^4)*(1+x^4)*(1+x+x^2+x^3+x^4)) + O(x^70)) \\ _Jinyuan Wang_, Feb 28 2020
%Y Cf. A309880, A309881, A309882.
%K nonn,easy
%O 0,8
%A _Wesley Ivan Hurt_, Aug 21 2019