A331200 Least number with each record number of factorizations into distinct factors > 1.

1, 6, 12, 24, 48, 60, 96, 120, 180, 240, 360, 480, 720, 840, 1080, 1260, 1440, 1680, 2160, 2520, 3360, 4320, 5040, 7560, 8640, 10080, 15120, 20160, 25200, 30240, 40320, 45360, 50400, 55440, 60480, 75600, 90720, 100800, 110880, 120960, 151200, 181440, 221760

Offset

1,2

Comments

First differs from A330997 in lacking 64.

Links

Giovanni Resta, Table of n, a(n) for n = 1..122

Jun Kyo Kim, On highly factorable numbers, Journal Of Number Theory, Vol. 72, No. 1 (1998), pp. 76-91.

Example

Strict factorizations of the initial terms:
  ()  (6)    (12)   (24)     (48)     (60)      (96)      (120)
      (2*3)  (2*6)  (3*8)    (6*8)    (2*30)    (2*48)    (2*60)
             (3*4)  (4*6)    (2*24)   (3*20)    (3*32)    (3*40)
                    (2*12)   (3*16)   (4*15)    (4*24)    (4*30)
                    (2*3*4)  (4*12)   (5*12)    (6*16)    (5*24)
                             (2*3*8)  (6*10)    (8*12)    (6*20)
                             (2*4*6)  (2*5*6)   (2*6*8)   (8*15)
                                      (3*4*5)   (3*4*8)   (10*12)
                                      (2*3*10)  (2*3*16)  (3*5*8)
                                                (2*4*12)  (4*5*6)
                                                          (2*3*20)
                                                          (2*4*15)
                                                          (2*5*12)
                                                          (2*6*10)
                                                          (3*4*10)
                                                          (2*3*4*5)

Mathematica

nn=1000;
strfacs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[strfacs[n/d], Min@@#>d&]], {d, Rest[Divisors[n]]}]];
qv=Table[Length[strfacs[n]], {n, nn}];
Table[Position[qv, i][[1, 1]], {i, Union[qv//.{foe___, x_, y_, afe___}/; x>y:>{foe, x, afe}]}]

Crossrefs

A subset of A330997.

All terms belong to A025487.

This is the strict version of highly factorable numbers A033833.

The corresponding records are A331232(n) = A045778(a(n)).

Factorizations are A001055 with image A045782 and complement A330976.

Strict factorizations are A045778 with image A045779 and complement A330975.

The least number with n strict factorizations is A330974(n).

The least number with A045779(n) strict factorizations is A045780(n)

Cf. A045783, A325238, A330972, A330973, A331023/A331024, A331201.

Sequence in context: A304938 A297107 A330997 * A212116 A160728 A332043

Adjacent sequences: A331197 A331198 A331199 * A331201 A331202 A331203

Keyword

nonn

Author

Gus Wiseman, Jan 12 2020

Extensions

a(37) and beyond from Giovanni Resta, Jan 17 2020

Status

approved