A284870 - OEIS

A284870

Expansion of Sum_{i>=1} i*x^i/(1 - x) * Product_{j=1..i} 1/(1 - x^j).

0, 1, 4, 10, 22, 42, 77, 131, 217, 345, 537, 812, 1211, 1767, 2547, 3615, 5078, 7043, 9687, 13185, 17815, 23867, 31766, 41972, 55146, 71997, 93519, 120813, 155358, 198811, 253374, 321509, 406436, 511802, 642264, 803140, 1001154, 1243966, 1541167, 1903754, 2345300, 2881404, 3531195, 4316632, 5264444, 6405389

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OFFSET

0,3

COMMENTS

Total number of parts in all partitions of all positive integers <= n.

Sum of largest parts of all partitions of all positive integers <= n.

From Omar E. Pol, Feb 16 2021: (Start)

Apart from initial zero this is as follows:

Convolution of A341062 and A014153.

Convolution of A000005 and A000070.

Convolution of nonzero terms of A006218 and A000041.

a(n) is also the total number of divisors of all terms in the n-th row of triangle A340581. These divisors are also all parts of all partitions of all positive integers <= n. (End)

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..10000

Index entries for related partition-counting sequences

FORMULA

G.f.: Sum_{i>=1} i*x^i/(1 - x) * Product_{j=1..i} 1/(1 - x^j).

G.f.: (1/(1 - x)) * Sum_{i>=1} x^i/(1 - x^i) * Product_{j>=1} 1/(1 - x^j).

a(n) = Sum_{k=0..n} A006128(k).

a(n) = A124920(n+1) - 1.

a(n) = Sum_{k=1..n} k * A299779(n,k). - Alois P. Heinz, May 14 2018

EXAMPLE

a(4) = 22 because we have 1 = 1, 2 = 2, 1 + 1 = 2, 3 = 3, 2 + 1 = 3, 1 + 1 + 1 = 3, 4 = 4, 3 + 1 = 4, 2 + 2 = 4, 2 + 1 + 1 = 4 and 1 + 1 + 1 + 1 = 4 therefore 1 + 1 + 2 + 1 + 2 + 3 + 1 + 2 + 2 + 3 + 4 = 22 (total number of parts) or 1 + 2 + 1 + 3 + 2 + 1 + 4 + 3 + 2 + 2 + 1 = 22 (sum of largest parts).

MAPLE

b:= proc(n, i) option remember; `if`(n=0 or i=1, [1, n],

b(n, i-1) +(p-> p+[0, p[1]])(b(n-i, min(n-i, i))))

end:

a:= proc(n) a(n):= `if`(n<1, 0, a(n-1)+b(n$2)[2]) end:

seq(a(n), n=0..45); # Alois P. Heinz, Feb 16 2021

MATHEMATICA

nmax = 45; CoefficientList[Series[Sum[i x^i /(1 - x) Product[1/(1 - x^j), {j, 1, i}], {i, 1, nmax}], {x, 0, nmax}], x]

nmax = 45; CoefficientList[Series[1/(1 - x) Sum[x^i /(1 - x^i), {i, 1, nmax}] Product[1/(1 - x^j), {j, 1, nmax}], {x, 0, nmax}], x]

Accumulate[Table[Sum[DivisorSigma[0, k] PartitionsP[n - k], {k, 1, n}], {n, 0, 45}]]

CROSSREFS

Cf. A000070, A006128, A015724, A026905, A124920, A138137, A182738, A299779.