A359678 Number of multisets (finite weakly increasing sequences of positive integers) with zero-based weighted sum (A359674) equal to n > 0.

1, 2, 4, 4, 6, 9, 8, 10, 14, 13, 16, 21, 17, 22, 28, 23, 30, 37, 30, 38, 46, 38, 46, 59, 46, 55, 70, 59, 70, 86, 67, 81, 96, 84, 98, 115, 95, 114, 135, 114, 132, 158, 127, 156, 178, 148, 176, 207, 172, 201, 227, 196, 228, 270, 222, 255, 296, 255, 295, 338, 278

Offset

1,2

Comments

The zero-based weighted sum of a sequence (y_1,...,y_k) is Sum_{i=1..k} (i-1)*y_i.

Links

Andrew Howroyd, Table of n, a(n) for n = 1..1000

Formula

G.f.: Sum_{k>=2} x^binomial(k,2)/((1 - x^binomial(k,2))*Product_{j=1..k-1} (1 - x^(binomial(k,2)-binomial(j,2)))). - Andrew Howroyd, Jan 22 2023

Example

The a(1) = 1 through a(8) = 10 multisets:
  {1,1}  {1,2}  {1,3}    {1,4}  {1,5}    {1,6}      {1,7}    {1,8}
         {2,2}  {2,3}    {2,4}  {2,5}    {2,6}      {2,7}    {2,8}
                {3,3}    {3,4}  {3,5}    {3,6}      {3,7}    {3,8}
                {1,1,1}  {4,4}  {4,5}    {4,6}      {4,7}    {4,8}
                                {5,5}    {5,6}      {5,7}    {5,8}
                                {1,1,2}  {6,6}      {6,7}    {6,8}
                                         {1,2,2}    {7,7}    {7,8}
                                         {2,2,2}    {1,1,3}  {8,8}
                                         {1,1,1,1}           {1,2,3}
                                                             {2,2,3}

Mathematica

zz[n_]:=Select[IntegerPartitions[n], UnsameQ@@#&&GreaterEqual @@ Differences[Append[#, 0]]&];
Table[Sum[Append[z, 0][[1]]-Append[z, 0][[2]], {z, zz[n]}], {n, 30}]

Prog

(PARI) seq(n)={Vec(sum(k=2, (sqrtint(8*n+1)+1)\2, my(t=binomial(k, 2)); x^t/((1-x^t)*prod(j=1, k-1, 1 - x^(t-binomial(j, 2)) + O(x^(n-t+1))))))} \\ Andrew Howroyd, Jan 22 2023

Crossrefs

The one-based version is A320387.

Number of appearances of n > 0 in A359674.

The sorted minimal ranks are A359675, reverse A359680.

The minimal ranks are A359676, reverse A359681.

The maximal ranks are A359757.

A053632 counts compositions by zero-based weighted sum.

A124757 gives zero-based weighted sums of standard compositions, rev A231204.

Cf. A029931, A243055, A304818, A358194, A359677.

Sequence in context: A241064 A292671 A210948 * A008133 A237828 A362607

Adjacent sequences: A359675 A359676 A359677 * A359679 A359680 A359681

Keyword

nonn

Author

Gus Wiseman, Jan 15 2023

Status

approved