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 A110618 #18 Aug 01 2019 00:07:48 %S A110618 1,0,1,1,3,3,7,8,15,18,30,37,58,71,105,131,186,230,318,393,530,653, %T A110618 863,1060,1380,1686,2164,2637,3345,4057,5096,6158,7665,9228,11395, %U A110618 13671,16765,20040,24418,29098,35251,41869,50460,59755,71669,84626,101050 %N A110618 Number of partitions of n with no part larger than n/2. Also partitions of n into n/2 or fewer parts. %C A110618 Also the number of integer partitions of n that are the vertex-degrees of some set multipartition (multiset of nonempty sets) with no singletons. - _Gus Wiseman_, Oct 30 2018 %F A110618 a(n) = A000041(n) - Sum_{i=0..floor((n-1)/2)} A000041(i) = A000041(n) - A000070(floor((n-1)/2)) = A110619(n, 2). %F A110618 a(2*n) = A209816(n). - _Gus Wiseman_, Oct 30 2018 %e A110618 a(5) = 3 since 5 can be partitioned as 1+1+1+1+1, 2+1+1+1, or 2+2+1; not counted are 5, 4+1, or 3+2. %e A110618 a(6) = 7 since 6 can be partitioned as 1+1+1+1+1+1, 1+1+1+1+2, 1+1+2+2, 2+2+2, 1+1+1+3, 1+2+3, 3+3; not counted are 1+1+4, 2+4, 1+5, 6. %e A110618 From _Gus Wiseman_, Oct 30 2018: (Start) %e A110618 The a(2) = 1 through a(8) = 15 partitions with no part larger than n/2: %e A110618 (11) (111) (22) (221) (33) (322) (44) %e A110618 (211) (2111) (222) (331) (332) %e A110618 (1111) (11111) (321) (2221) (422) %e A110618 (2211) (3211) (431) %e A110618 (3111) (22111) (2222) %e A110618 (21111) (31111) (3221) %e A110618 (111111) (211111) (3311) %e A110618 (1111111) (4211) %e A110618 (22211) %e A110618 (32111) %e A110618 (41111) %e A110618 (221111) %e A110618 (311111) %e A110618 (2111111) %e A110618 (11111111) %e A110618 The a(2) = 1 through a(8) = 15 partitions into n/2 or fewer parts: %e A110618 (2) (3) (4) (5) (6) (7) (8) %e A110618 (22) (32) (33) (43) (44) %e A110618 (31) (41) (42) (52) (53) %e A110618 (51) (61) (62) %e A110618 (222) (322) (71) %e A110618 (321) (331) (332) %e A110618 (411) (421) (422) %e A110618 (511) (431) %e A110618 (521) %e A110618 (611) %e A110618 (2222) %e A110618 (3221) %e A110618 (3311) %e A110618 (4211) %e A110618 (5111) %e A110618 The a(6) = 7 integer partitions of 6 with no part larger than n/2 together with a realizing set multipartition of each (the parts of the partition count the appearances of each vertex in the set multipartition): %e A110618 (33): {{1,2},{1,2},{1,2}} %e A110618 (321): {{1,2},{1,2},{1,3}} %e A110618 (3111): {{1,2},{1,3},{1,4}} %e A110618 (222): {{1,2,3},{1,2,3}} %e A110618 (2211): {{1,2},{1,2,3,4}} %e A110618 (21111): {{1,2},{1,3,4,5}} %e A110618 (111111): {{1,2,3,4,5,6}} %e A110618 (End) %p A110618 A000070 := proc(n) add( combinat[numbpart](i),i=0..n) ; end proc: %p A110618 A110618 := proc(n) combinat[numbpart](n) - A000070(floor((n-1)/2)) ; end proc: # _R. J. Mathar_, Jan 24 2011 %t A110618 f[n_, 1] := 1; f[1, k_] := 1; f[n_, k_] := f[n, k] = If[k > n, f[n, k - 1], f[n, k - 1] + f[n - k, k]]; g[n_] := f[n, Floor[n/2]]; g[0] = 1; g[1] = 0; Array[g, 47, 0] (* _Robert G. Wilson v_, Jan 23 2011 *) %t A110618 sps[{}]:={{}};sps[set:{i_,___}]:=Join@@Function[s,Prepend[#,s]&/@sps[Complement[set,s]]]/@Cases[Subsets[set],{i,___}]; %t A110618 mps[set_]:=Union[Sort[Sort/@(#/.x_Integer:>set[[x]])]&/@sps[Range[Length[set]]]]; %t A110618 multhyp[m_]:=Select[mps[m],And[And@@UnsameQ@@@#,Min@@Length/@#>1]&]; %t A110618 strnorm[n_]:=Flatten[MapIndexed[Table[#2,{#1}]&,#]]&/@IntegerPartitions[n]; %t A110618 Table[Length[Select[strnorm[n],multhyp[#]!={}&]],{n,8}] (* _Gus Wiseman_, Oct 30 2018 *) %o A110618 (PARI) a(n) = numbpart(n) - sum(i=0, if (n%2, n\2, n/2-1), numbpart(i)); \\ _Michel Marcus_, Oct 31 2018 %Y A110618 Cf. A000070, A000569, A025065, A049311, A096373, A116540, A147878, A209816, A283877, A306005, A320921. %K A110618 nonn %O A110618 0,5 %A A110618 _Henry Bottomley_, Aug 01 2005