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 A321441 Number of "hexagonal partitions" of n 3

%I

%S 1,1,2,3,4,4,6,5,7,8,8,7,11,8,12,12,11,10,16,12,15,15,14,14,22,14,18,

%T 18,18,20,24,14,21,24,24,22,28,15,26,29,24,22,32,24,31,30,24,26,37,28,

%U 34,29,29,31,46,25,35,36,28,38,45,30,38,42,40,35,46,26

%N Number of "hexagonal partitions" of n

%C A "hexagonal partition" is one whose parts are consecutive, whose largest part has arbitrary multiplicity, and the remaining parts have multiplicity 1 or 2, with the single parts smaller than the double parts.

%C Each of the hexagonal diagrams counted by A116513 corresponds to at most three of these partitions, so this sequence is bounded above by 3*A116513. The relationship between A116513 and this sequence would bear further study.

%C The partitions counted here are a superset of those counted at A321440.

%H Chai Wah Wu, <a href="/A321441/b321441.txt">Table of n, a(n) for n = 0..10000</a>

%e Here are the derivations of the terms up through n = 10. Partitions are abbreviated as strings of digits.

%e n = 0: (empty partition)

%e n = 1: 1

%e n = 2: 11, 2

%e n = 3: 111, 12, 3

%e n = 4: 1111, 112, 22, 4

%e n = 5: 11111, 122, 23, 5

%e n = 6: 111111, 1122, 123, 222, 33, 6

%e n = 7: 1111111, 1222, 223, 34, 7

%e n = 8: 11111111, 11222, 1223, 2222, 233, 44, 8

%e n = 9: 111111111, 11223, 12222, 1233, 234, 333, 45, 9

%e n = 10: 1111111111, 112222, 1234, 22222, 2233, 334, 55, (10)

%o (Python)

%o from __future__ import division

%o def A321441(n):

%o if n == 0:

%o return 1

%o c = 0

%o for i in range(n):

%o mi = n + i*(i+1)//2

%o for j in range(i,n):

%o mj = mi + j*(j+1)//2

%o for k in range(j+1,n+1):

%o r = mj - k*k

%o if r < 0:

%o break

%o if not r % k:

%o c += 1

%o return c # _Chai Wah Wu_, Nov 11 2018

%Y Counted partitions are a generalization of those counted at A312440. This sequence has an application to A116513.

%K nonn

%O 0,3

%A _Allan C. Wechsler_, Nov 09 2018

%E More terms from _Chai Wah Wu_, Nov 11 2018

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Last modified July 31 08:38 EDT 2021. Contains 346369 sequences. (Running on oeis4.)