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 A321443 Number of "bilaterally symmetric hexagonal partitions" of n 2
 1, 1, 2, 2, 4, 2, 5, 3, 5, 4, 7, 2, 8, 4, 7, 5, 9, 2, 11, 5, 8, 5, 10, 4, 13, 6, 8, 5, 13, 4, 16, 4, 8, 8, 14, 5, 16, 5, 11, 7, 16, 2, 17, 9, 12, 8, 13, 4, 20, 8, 14, 7, 15, 5, 22, 7, 11, 8, 20, 4, 23, 8, 10, 11, 20, 7, 20, 4, 17, 9, 24, 5, 22, 7, 13, 13, 16 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS A bilaterally symmetric hexagonal partition is one whose parts are consecutive integers, of which all have multiplicity 2 except the largest part, which may have any multiplicity (including 1). This is a restriction of the concept of hexagonal partition presented in A321441. The nomenclature is suggested by presenting such partitions as hexagonal patches of the triangular lattice A2. LINKS Chai Wah Wu, Table of n, a(n) for n = 0..10000 EXAMPLE Here are the derivations of the terms up through n = 10. Partitions are abbreviated as strings of digits. n = 0: (empty partition) n = 1: 1 n = 2: 11, 2 n = 3: 111, 3 n = 4: 1111, 112, 22, 4 n = 5: 11111, 5 n = 6: 111111, 1122, 222, 33, 6 n = 7: 1111111, 223, 7 n = 8: 11111111, 11222, 2222, 44, 8 n = 9: 111111111, 11223, 333, 9 n = 10: 1111111111, 112222, 22222, 2233, 334, 55, (10) PROG (Python) def A321443(n):     if n == 0:         return 1     c = 0     for i in range(n):         mi = i*(i+1) + n         for j in range(i+1, n+1):             k = mi - j*j             if k < 0:                 break             if not k % j:                 c += 1     return c # Chai Wah Wu, Nov 10 2018 CROSSREFS A321441 counts hexagonal partitions in general. A321440 counts a different special kind of hexagonal partition. A116513 counts hexagonal "diagrams", of which these partitions are a sort of projection. Sequence in context: A187782 A129296 A300837 * A333836 A125296 A294097 Adjacent sequences:  A321440 A321441 A321442 * A321444 A321445 A321446 KEYWORD nonn AUTHOR Allan C. Wechsler, Nov 09 2018 EXTENSIONS More terms from Chai Wah Wu, Nov 10 2018 STATUS approved

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Last modified July 27 08:33 EDT 2021. Contains 346304 sequences. (Running on oeis4.)