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A033461
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Number of partitions of n into distinct squares.
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108
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1, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 2, 2, 0, 0, 2, 2, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 2, 1, 0, 0, 2, 2, 0, 0, 2, 3, 1, 1, 2, 2, 1, 1, 1, 1, 1, 0, 2, 3, 1, 1, 4, 3, 0, 1, 2, 2, 1, 0, 1, 4, 3, 0, 2, 4, 2, 1, 3, 2, 1, 2, 3, 3, 2, 1, 3, 6, 3, 0, 2, 5, 3, 0, 1, 3, 3, 3, 4
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OFFSET
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0,26
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COMMENTS
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"WEIGH" transform of squares A000290.
Number of partitions of n in which each part i has multiplicity i. Example: a(50)=3 because we have [1,2,2,3,3,3,6,6,6,6,6,6], [1,7,7,7,7,7,7,7], and [3,3,3,4,4,4,4,5,5,5,5,5]. - Emeric Deutsch, Jan 26 2016
The Heinz numbers of integer partitions into distinct pairs are given by A324587. - Gus Wiseman, Mar 09 2019
Equivalent to Emeric Deutsch's comment, a(n) is the number of integer partitions of n where the multiplicities (where if x < y the multiplicity of x is counted prior to the multiplicity of y) are equal to the distinct parts in increasing order. The Heinz numbers of these partitions are given by A109298. For example, the first 30 terms count the following integer partitions:
1: (1)
4: (22)
5: (221)
9: (333)
10: (3331)
13: (33322)
14: (333221)
16: (4444)
17: (44441)
20: (444422)
21: (4444221)
25: (55555)
25: (4444333)
26: (555551)
26: (44443331)
29: (5555522)
29: (444433322)
30: (55555221)
30: (4444333221)
The case where the distinct parts are taken in decreasing order is A324572, with Heinz numbers given by A324571.
(End)
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LINKS
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FORMULA
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G.f.: Product_{n>=1} ( 1+x^(n^2) ).
a(n) ~ exp(3 * 2^(-5/3) * Pi^(1/3) * ((sqrt(2)-1)*zeta(3/2))^(2/3) * n^(1/3)) * ((sqrt(2)-1)*zeta(3/2))^(1/3) / (2^(4/3) * sqrt(3) * Pi^(1/3) * n^(5/6)), where zeta(3/2) = A078434. - Vaclav Kotesovec, Dec 09 2016
See Murthy, Brack, Bhaduri, Bartel (2018) for a more complete asymptotic expansion. - N. J. A. Sloane, Aug 17 2018
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EXAMPLE
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a(50)=3 because we have [1,4,9,36], [1,49], and [9,16,25]. - Emeric Deutsch, Jan 26 2016
The first 30 terms count the following integer partitions:
1: (1)
4: (4)
5: (4,1)
9: (9)
10: (9,1)
13: (9,4)
14: (9,4,1)
16: (16)
17: (16,1)
20: (16,4)
21: (16,4,1)
25: (25)
25: (16,9)
26: (25,1)
26: (16,9,1)
29: (25,4)
29: (16,9,4)
30: (25,4,1)
30: (16,9,4,1)
(End)
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MAPLE
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b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0,
b(n, i-1) +`if`(i^2>n, 0, b(n-i^2, i-1))))
end:
a:= n-> b(n, isqrt(n)):
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MATHEMATICA
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nn=10; CoefficientList[Series[Product[(1+x^(k*k)), {k, nn}], {x, 0, nn*nn}], x] (* T. D. Noe, Jul 24 2006 *)
b[n_, i_] := b[n, i] = If[n==0, 1, If[i<1, 0, b[n, i-1] + If[i^2 > n, 0, b[n - i^2, i-1]]]]; a[n_] := b[n, Floor[Sqrt[n]]]; Table[a[n], {n, 0, 100}] (* Jean-François Alcover, Sep 21 2015, after Alois P. Heinz *)
nmax = 20; poly = ConstantArray[0, nmax^2 + 1]; poly[[1]] = 1; poly[[2]] = 1; Do[Do[poly[[j + 1]] += poly[[j - k^2 + 1]], {j, nmax^2, k^2, -1}]; , {k, 2, nmax}]; poly (* Vaclav Kotesovec, Dec 09 2016 *)
Table[Length[Select[IntegerPartitions[n], Reverse[Union[#]]==Length/@Split[#]&]], {n, 30}] (* Gus Wiseman, Mar 09 2019 *)
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PROG
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(PARI) a(n)=polcoeff(prod(k=1, sqrt(n), 1+x^k^2), n)
(Python)
from functools import cache
from sympy.core.power import isqrt
@cache
def b(n, i):
if n == 0: return 1
if i == 0: return 0
i2 = i*i
return b(n, i-1) + (0 if i2 > n else b(n - i2, i-1))
a = lambda n: b(n, isqrt(n))
print([a(n) for n in range(1, 101)]) # Darío Clavijo, Nov 30 2023
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CROSSREFS
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Cf. A001156 (non-strict case), A001462, A005117, A052335, A078135, A109298, A114638, A117144, A324571, A324572, A324587, A324588.
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KEYWORD
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nonn,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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