This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A332836 #15 Dec 31 2020 17:00:13 %S A332836 1,1,2,4,7,12,24,40,73,128,230,399,712,1241,2192,3833,6746,11792, %T A332836 20711,36230,63532,111163,194782,340859,596961,1044748,1829241, %U A332836 3201427,5604504,9808976,17170112,30051470,52601074,92063629,161140256,282033124,493637137,863982135,1512197655 %N A332836 Number of compositions of n whose run-lengths are weakly increasing. %C A332836 A composition of n is a finite sequence of positive integers summing to n. %C A332836 Also compositions whose run-lengths are weakly decreasing. %H A332836 Andrew Howroyd, <a href="/A332836/b332836.txt">Table of n, a(n) for n = 0..1000</a> %e A332836 The a(0) = 1 through a(5) = 12 compositions: %e A332836 () (1) (2) (3) (4) (5) %e A332836 (11) (12) (13) (14) %e A332836 (21) (22) (23) %e A332836 (111) (31) (32) %e A332836 (121) (41) %e A332836 (211) (122) %e A332836 (1111) (131) %e A332836 (212) %e A332836 (311) %e A332836 (1211) %e A332836 (2111) %e A332836 (11111) %e A332836 For example, the composition (2,3,2,2,1,1,2,2,2) has run-lengths (1,1,2,2,3) so is counted under a(17). %t A332836 Table[Length[Select[Join@@Permutations/@IntegerPartitions[n],LessEqual@@Length/@Split[#]&]],{n,0,10}] %o A332836 (PARI) %o A332836 step(M, m)={my(n=matsize(M)[1]); for(p=m+1, n, my(v=vector((p-1)\m, i, M[p-i*m,i]), s=vecsum(v)); M[p,]+=vector(#M,i,s-if(i<=#v, v[i]))); M} %o A332836 seq(n)={my(M=matrix(n+1, n, i, j, i==1)); for(m=1, n, M=step(M, m)); M[1,n]=0; vector(n+1, i, vecsum(M[i,]))/(n-1)} \\ _Andrew Howroyd_, Dec 31 2020 %Y A332836 The version for the compositions themselves (not run-lengths) is A000041. %Y A332836 The case of partitions is A100883. %Y A332836 The case of unsorted prime signature is A304678, with dual A242031. %Y A332836 Permitting the run-lengths to be weakly decreasing also gives A332835. %Y A332836 The complement is counted by A332871. %Y A332836 Unimodal compositions are A001523. %Y A332836 Compositions that are not unimodal are A115981. %Y A332836 Compositions with equal run-lengths are A329738. %Y A332836 Compositions whose run-lengths are unimodal are A332726. %Y A332836 Cf. A001462, A072704, A072706, A100882, A181819, A329744, A329766, A332641, A332727, A332745, A332833, A332834. %K A332836 nonn %O A332836 0,3 %A A332836 _Gus Wiseman_, Feb 29 2020 %E A332836 Terms a(21) and beyond from _Andrew Howroyd_, Dec 30 2020