cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-10 of 12 results. Next

A045782 Number of factorizations of n for some n (image of A001055).

Original entry on oeis.org

1, 2, 3, 4, 5, 7, 9, 11, 12, 15, 16, 19, 21, 22, 26, 29, 30, 31, 36, 38, 42, 45, 47, 52, 56, 57, 64, 66, 67, 74, 77, 92, 97, 98, 101, 105, 109, 118, 135, 137, 139, 141, 162, 165, 171, 176, 181, 189, 195, 198, 203, 212, 231, 249, 250, 254, 257, 267, 269, 272, 289
Offset: 1

Views

Author

David W. Wilson

Keywords

Comments

Also the image of A318284. - Gus Wiseman, Jan 11 2020

Links

Crossrefs

Factorizations are A001055 with image this sequence and complement A330976.
Strict factorizations are A045778 with image A045779 and complement A330975.
The least number with exactly a(n) factorizations is A045783(n).
The least number with exactly n factorizations is A330973(n).
Cf. A002033, A007716, A033833, A318284, A325238, A330935, A330936, A330977, A330989, A330991, A330992, A330997.

Programs

  • Mathematica
    terms = 61; m0 = 10^5; dm = 10^4;
f[1, ] = 1; f[n, k_] := f[n, k] = Sum[f[n/d, d], {d, Select[Divisors[n], 1 < # <= k &]}];
Clear[seq]; seq[m_] := seq[m] = Sort[Tally[Table[f[n, n], {n, 1, m}]][[All, 1]]][[1 ;; terms]]; seq[m = m0]; seq[m += dm]; While[Print[m]; seq[m] != seq[m - dm], m += dm];
seq[m] (* Jean-François Alcover, Oct 04 2018 *)

Formula

The Luca et al. paper shows that the number of terms with a(n) <= x is x^{ O( log log log x / log log x )}. - N. J. A. Sloane, Jun 12 2009

Extensions

Name edited by Gus Wiseman, Jan 11 2020

A045783 Least value with A045782(n) factorizations.

Original entry on oeis.org

1, 4, 8, 12, 16, 24, 36, 60, 48, 128, 72, 96, 120, 256, 180, 144, 192, 216, 420, 240, 1024, 384, 288, 360, 2048, 432, 480, 900, 768, 840, 576, 1260, 864, 720, 8192, 960, 1080, 1152, 4620, 1800, 3072, 1680, 1728, 1920, 1440, 32768, 2304, 2592, 6144
Offset: 1

Views

Author

David W. Wilson

Keywords

Examples

			From _Gus Wiseman_, Jan 11 2020: (Start)
Factorizations of n = 1, 4, 8, 12, 16, 24, 36, 60, 48:
  {}  4    8      12     16       24       36       60       48
      2*2  2*4    2*6    2*8      3*8      4*9      2*30     6*8
           2*2*2  3*4    4*4      4*6      6*6      3*20     2*24
                  2*2*3  2*2*4    2*12     2*18     4*15     3*16
                         2*2*2*2  2*2*6    3*12     5*12     4*12
                                  2*3*4    2*2*9    6*10     2*3*8
                                  2*2*2*3  2*3*6    2*5*6    2*4*6
                                           3*3*4    3*4*5    3*4*4
                                           2*2*3*3  2*2*15   2*2*12
                                                    2*3*10   2*2*2*6
                                                    2*2*3*5  2*2*3*4
                                                             2*2*2*2*3
(End)

Links

Crossrefs

All terms belong to A025487.
The strict version is A045780.
The sorted version is A330972.
Includes all highly factorable numbers A033833.
The least number with exactly n factorizations is A330973(n).
Factorizations are A001055 with image A045782 and complement A330976.
Strict factorizations are A045778 with image A045779 and complement A330975.
Cf. A070175, A318284, A325238, A330974, A330989, A330992, A330998.

A330976 Numbers that are not the number of factorizations into factors > 1 of any positive integer.

Original entry on oeis.org

6, 8, 10, 13, 14, 17, 18, 20, 23, 24, 25, 27, 28, 32, 33, 34, 35, 37, 39, 40, 41, 43, 44, 46, 48, 49, 50, 51, 53, 54, 55, 58, 59, 60, 61, 62, 63, 65, 68, 69, 70, 71, 72, 73, 75, 76, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 93, 94, 95, 96, 99
Offset: 1

Views

Author

Gus Wiseman, Jan 07 2020

Keywords

Comments

Warning: I have only confirmed the first eight terms. The rest are derived from A045782. - Gus Wiseman, Jan 07 2020

Links

Crossrefs

Complement of A045782.
The strict version is A330975.
Factorizations are A001055, with image A045782.
Strict factorizations are A045778, with image A045779.
The least number with n factorizations is A330973(n).
Cf. A033833, A045779, A045783, A317145, A330935, A330972, A330974, A330977, A330991.

Programs

  • Mathematica
    nn=15;
fam[n_]:=fam[n]=If[n<=1,{{}},Join@@Table[Map[Prepend[#,d]&,Select[fam[n/d],Min@@#>=d&]],{d,Rest[Divisors[n]]}]];
nds=Length/@Array[fam[#]&,2^nn];
Complement[Range[nn],nds]

A045779 Number of factorizations of n into distinct factors for some n (image of A045778).

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 17, 18, 19, 21, 22, 25, 27, 31, 32, 33, 34, 38, 40, 42, 43, 44, 46, 52, 54, 55, 56, 57, 59, 61, 64, 67, 70, 74, 76, 80, 83, 88, 89, 91, 93, 100, 104, 110, 111, 112, 116, 117, 120, 122, 123, 132, 137, 140, 141, 142, 143, 148
Offset: 1

Views

Author

David W. Wilson

Keywords

Comments

We may use A045778(k*m) >= A045778(k) for any k, m >= 1 to disprove presence of some positive integer in this sequence. - David A. Corneth, Oct 24 2024

Examples

			From _David A. Corneth_, Oct 24 2024: (Start)
5 is a term as 24 has five factorizations into distinct divisors of 24 namely 24 = 2 * 12 = 3 * 8 = 4 * 6 = 2 * 3 * 4 which is five such factorizations.
11 is not a term. From terms in A025487 only the numbers 2, 4, 6, 8, 12, 16, 24, 30, 32, 36, 48, 60, 64, 72, 96, 128, 256, 512, 1024 have no more than 11 such factorizations. Any multiple of these numbers in A025487 that is not already listed has more than 11 such factorizations which proves 11 is not in this sequence. (End)

Links

Crossrefs

Factorizations are A001055, with image A045782, with complement A330976.
Strict factorizations are A045778 with image A045779 and complement A330975.
The least number with A045779(n) strict factorizations is A045780(n).
The least number with n strict factorizations is A330974(n).
Cf. A001222, A025487, A033833, A045783, A318286, A328966, A330972, A330973, A330997.

Extensions

Name edited by Gus Wiseman, Jan 11 2020

A045780 Least value with A045779(n) factorizations into distinct factors.

Original entry on oeis.org

1, 6, 12, 64, 24, 256, 48, 512, 60, 96, 2048, 144, 210, 120, 216, 180, 384, 288, 16384, 240, 432, 420, 65536, 1536, 360, 480, 900, 864, 3072, 1152, 1296, 2310, 524288, 6144, 960, 720, 840, 2304, 1728, 1080, 1260, 2592, 2097152, 1800, 4608, 24576, 4194304, 1440, 3456
Offset: 1

Views

Author

David W. Wilson

Keywords

Examples

			From _Gus Wiseman_, Jan 11 2020: (Start)
The strict factorizations of a(n) for n = 1..9:
  ()  (6)    (12)   (64)     (24)     (256)     (48)     (512)     (60)
      (2*3)  (2*6)  (2*32)   (3*8)    (4*64)    (6*8)    (8*64)    (2*30)
             (3*4)  (4*16)   (4*6)    (8*32)    (2*24)   (16*32)   (3*20)
                    (2*4*8)  (2*12)   (2*128)   (3*16)   (2*256)   (4*15)
                             (2*3*4)  (2*4*32)  (4*12)   (4*128)   (5*12)
                                      (2*8*16)  (2*3*8)  (2*4*64)  (6*10)
                                                (2*4*6)  (2*8*32)  (2*5*6)
                                                         (4*8*16)  (3*4*5)
                                                                   (2*3*10)
(End)
30 is not in the sequence even though A045779(30) = 5. As 24 is the smallest k such that A045779(k) = 5 we have a(m) = 24 where m is such that A045779(m) = 5 which turns out to be m = 5 (not every positive integer is in A045779). So a(5) = 24. - _David A. Corneth_, Oct 24 2024

Links

Crossrefs

All terms belong to A025487.
The non-strict version is A045783.
The sorted version is A330997.
Factorizations are A001055 with image A045782 and complement A330976.
Strict factorizations are A045778 with image A045779 and complement A330975.
The least number with exactly n strict factorizations is A330974(n).
Cf. A033833, A318286, A330972, A330973, A330989.

Extensions

More terms from David A. Corneth, Oct 24 2024

A330974 Least positive integer with n factorizations into distinct factors > 1, and 0 if no such number exists.

Original entry on oeis.org

1, 6, 12, 64, 24, 256, 48, 512, 60, 96, 0, 2048, 0, 144, 210, 120, 216, 180, 384, 0, 288, 16384, 0, 0, 240, 0, 432, 0, 0, 0, 420, 65536, 1536, 360, 0, 0, 0, 480, 0, 900, 0, 864, 3072, 1152, 0, 1296, 0, 0, 0, 0, 0, 2310, 0, 524288, 6144, 960, 720, 0, 840, 0, 2304
Offset: 1

Views

Author

Gus Wiseman, Jan 06 2020

Keywords

Crossrefs

All nonzero terms belong to A025487.
Strict factorizations are A045778, with image A045779.
The version with zeros removed is A045780.
The non-strict version is A330973.
Positions of zeros are A330975.
The sorted version is A330997.
Cf. A001055, A001222, A033833, A045782, A045783, A318286, A328966, A330972.

Programs

  • Mathematica
    nn=10;
fam[n_]:=fam[n]=If[n<=1,{{}},Join@@Table[Map[Prepend[#,d]&,Select[fam[n/d],Min@@#>=d&]],{d,Rest[Divisors[n]]}]];
nds=Length/@Array[Select[fam[#],UnsameQ@@#&]&,2^nn];
Table[If[#=={},0,#[[1,1]]]&[Position[nds,i]],{i,nn}]

Extensions

More terms from Jinyuan Wang, Jul 07 2021

A330997 Sorted list containing the least number with each possible nonzero number of factorizations into distinct factors > 1.

Original entry on oeis.org

1, 6, 12, 24, 48, 60, 64, 96, 120, 144, 180, 210, 216, 240, 256, 288, 360, 384, 420, 432, 480, 512, 720, 840, 864, 900, 960, 1080, 1152, 1260, 1296, 1440, 1536, 1680, 1728, 1800, 2048, 2160, 2304, 2310, 2520, 2592, 2880, 3072, 3360, 3456, 3600, 3840, 4320
Offset: 1

Views

Author

Gus Wiseman, Jan 06 2020

Keywords

Examples

			The strict factorizations of a(n) for n = 1..9.
  {}  6    12   24     48     60      64     96      120
      2*3  2*6  3*8    6*8    2*30    2*32   2*48    2*60
           3*4  4*6    2*24   3*20    4*16   3*32    3*40
                2*12   3*16   4*15    2*4*8  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

Crossrefs

All terms belong to A025487.
Strict factorizations are A045778, with image A045779.
The unsorted version is A045780.
The non-strict version is A330972.
The least number with n strict factorizations is A330974.
Cf. A001055, A001222, A033833, A045782, A318286, A325238, A330935, A330973, A330975.

Programs

  • Mathematica
    nn=1000;
strfacs[n_]:=If[n<=1,{{}},Join@@Table[Map[Prepend[#,d]&,Select[strfacs[n/d],Min@@#>d&]],{d,Rest[Divisors[n]]}]];
nds=Length/@Array[strfacs,nn];
Table[Position[nds,i][[1,1]],{i,First/@Gather[nds]}]

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

Original entry on oeis.org

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

Views

Author

Gus Wiseman, Jan 12 2020

Keywords

Comments

First differs from A330997 in lacking 64.

Examples

			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)

Links

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.

Programs

  • 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}]}]

Extensions

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

A331232 Record numbers of factorizations into distinct factors > 1.

Original entry on oeis.org

1, 2, 3, 5, 7, 9, 10, 16, 18, 25, 34, 38, 57, 59, 67, 70, 91, 100, 117, 141, 161, 193, 253, 296, 306, 426, 552, 685, 692, 960, 1060, 1067, 1216, 1220, 1589, 1591, 1912, 2029, 2157, 2524, 2886, 3249, 3616, 3875, 4953, 5147, 5285, 5810, 6023, 6112, 6623, 8129
Offset: 1

Views

Author

Gus Wiseman, Jan 12 2020

Keywords

Examples

			Representatives for the initial records and their strict factorizations:
  ()  (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)

Links

Crossrefs

The non-strict version is A272691.
The first appearance of a(n) in A045778 is at index A331200(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. A033833, A045783, A325238, A330972, A330973, A330997, A331023/A331024, A331201.

Programs

  • 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}];
Union[qv//.{foe___,x_,y_,afe___}/;x>y:>{foe,x,afe}]
  • Python
    def fact(num):
    ret = []
    temp = num
    div = 2
    while temp > 1:
        while temp % div == 0:
            ret.append(div)
            temp //= div
        div += 1
    return ret
def all_partitions(lst):
    if lst:
        x = lst[0]
        for partition in all_partitions(lst[1:]):
            yield [x] + partition
            for i, _ in enumerate(partition):
                partition[i] *= x
                yield partition
                partition[i] //= x
    else:
        yield []
best = 0
terms = [0]
q = 2
while len(terms) < 100:
    total_set = set()
    factors = fact(q)
    total_set = set(tuple(sorted(x)) for x in all_partitions(factors) if len(x) == len(set(x)))
    if len(total_set) > best:
        best = len(total_set)
        terms.append(best)
        print(q,best)
    q += 2#only check evens
print(terms)
#  David Consiglio, Jr., Jan 14 2020

Formula

a(n) = A045778(A331200(n)).

Extensions

a(26)-a(37) from David Consiglio, Jr., Jan 14 2020
a(38) and beyond from Giovanni Resta, Jan 17 2020

A331201 Numbers k such that the number of factorizations of k into distinct factors > 1 is a prime number.

Original entry on oeis.org

6, 8, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 50, 51, 52, 54, 55, 56, 57, 58, 62, 63, 65, 66, 68, 69, 70, 74, 75, 76, 77, 78, 80, 81, 82, 85, 86, 87, 88, 91, 92, 93, 94, 95, 98, 99, 100, 102
Offset: 1

Views

Author

Gus Wiseman, Jan 12 2020

Keywords

Comments

First differs from A080257 in lacking 60.

Examples

			Strict factorizations of selected terms:
  (6)    (12)   (24)     (48)     (216)
  (2*3)  (2*6)  (3*8)    (6*8)    (3*72)
         (3*4)  (4*6)    (2*24)   (4*54)
                (2*12)   (3*16)   (6*36)
                (2*3*4)  (4*12)   (8*27)
                         (2*3*8)  (9*24)
                         (2*4*6)  (12*18)
                                  (2*108)
                                  (3*8*9)
                                  (4*6*9)
                                  (2*3*36)
                                  (2*4*27)
                                  (2*6*18)
                                  (2*9*12)
                                  (3*4*18)
                                  (3*6*12)
                                  (2*3*4*9)

Crossrefs

The version for strict integer partitions is A035359.
The version for integer partitions is A046063.
The version for set partitions is A051130.
The non-strict version is A330991.
Factorizations are A001055 with image A045782 and complement A330976.
Strict factorizations are A045778 with image A045779 and complement A330975.
Numbers whose number of strict factorizations is odd are A331230.
Numbers whose number of strict factorizations is even are A331231.
The least number with n strict factorizations is A330974(n).
Cf. A001318, A045780, A318286, A328966, A330992, A330993, A330997, A331023/A331024, A331050, A331051, A331200, A331232.

Programs

  • Mathematica
    strfacs[n_]:=If[n<=1,{{}},Join@@Table[Map[Prepend[#,d]&,Select[strfacs[n/d],Min@@#>d&]],{d,Rest[Divisors[n]]}]];
Select[Range[100],PrimeQ[Length[strfacs[#]]]&]
Showing 1-10 of 12 results. Next

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement.