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A272691
Number of factorizations of the highly factorable numbers A033833.
3
1, 2, 3, 4, 5, 7, 9, 12, 16, 19, 21, 29, 30, 31, 38, 47, 52, 57, 64, 77, 98, 105, 109, 118, 171, 212, 289, 382, 392, 467, 484, 662, 719, 737, 783, 843, 907, 1097, 1261, 1386, 1397, 1713, 1768, 2116, 2179, 2343, 3079, 3444, 3681, 3930, 5288, 5413, 5447
OFFSET
1,2
COMMENTS
These are defined as record numbers of factorizations (A001055). - Gus Wiseman, Jan 13 2020
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..235 (terms 1..118 from E. R. Canfield et al.)
R. E. Canfield, P. Erdős and C. Pomerance, On a Problem of Oppenheim concerning "Factorisatio Numerorum", J. Number Theory 17 (1983), 1-28.
Jun Kyo Kim, On highly factorable numbers, Journal Of Number Theory, Vol. 72, No. 1 (1998), pp. 76-91.
FORMULA
a(n) = A001055(A033833(n)).
a(n) = A033834(n) + 1. - Amiram Eldar, Jun 07 2019
EXAMPLE
From Gus Wiseman, Jan 13 2020: (Start)
The a(1) = 1 through a(8) = 12 factorizations of highly factorable numbers:
() (4) (8) (12) (16) (24) (36) (48)
(2*2) (2*4) (2*6) (2*8) (3*8) (4*9) (6*8)
(2*2*2) (3*4) (4*4) (4*6) (6*6) (2*24)
(2*2*3) (2*2*4) (2*12) (2*18) (3*16)
(2*2*2*2) (2*2*6) (3*12) (4*12)
(2*3*4) (2*2*9) (2*3*8)
(2*2*2*3) (2*3*6) (2*4*6)
(3*3*4) (3*4*4)
(2*2*3*3) (2*2*12)
(2*2*2*6)
(2*2*3*4)
(2*2*2*2*3)
(End)
MATHEMATICA
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
Table[Length[facs[n]], {n, 100}]//.{foe___, x_, y_, afe___}/; x>=y:>{foe, x, afe} (* Gus Wiseman, Jan 13 2020 *)
CROSSREFS
The strict version is A331232.
Factorizations are A001055, with image A045782 and complement A330976.
Highly factorable numbers are A033833, with strict version A331200.
Sequence in context: A039861 A039877 A291833 * A192433 A189083 A318156
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jun 02 2016, following a suggestion from George Beck.
STATUS
approved