A050370 -id:A050370 - cp's OEIS frontend

A114591 A composite analog of the Moebius function: Sum_{n>=1} a(n)/n^s = Product_{c=composites} (1 - 1/c^s) = zeta(s) *Product_{k>=2} (1 - 1/k^s).

1, 0, 0, -1, 0, -1, 0, -1, -1, -1, 0, -1, 0, -1, -1, -1, 0, -1, 0, -1, -1, -1, 0, 0, -1, -1, -1, -1, 0, -1, 0, 0, -1, -1, -1, 0, 0, -1, -1, 0, 0, -1, 0, -1, -1, -1, 0, 1, -1, -1, -1, -1, 0, 0, -1, 0, -1, -1, 0, 1, 0, -1, -1, 0, -1, -1, 0, -1, -1, -1, 0, 2, 0, -1, -1, -1, -1, -1, 0, 1

Offset: 1

Leroy Quet, Dec 11 2005

sign

For n >= 2, Sum_{k|n} A050370(n/k) * a(k) = 0.
Sum_{n>=1} a(n)/n^2 = Pi^2/12.
a(n) = Sum_{k|n} A114592(k).

			24 can be factored into distinct composites as 24 and as 4*6.
So a(24) = (-1)^1 + (-1)^2 = 0, where the 1 exponent is due to the 1 factor of the 24 = 24 factorization and the 2 exponent is due to the 2 factors of the 24 = 4*6 factorization.

Antti Karttunen, Table of n, a(n) for n = 1..10000
Index entries for sequences computed from exponents in factorization of n

Cf. A045778, A050370, A114592.

a[n_] := Total[((-1)^Length[#]& ) /@ Select[Subsets[Select[Rest[Divisors[n]], !PrimeQ[#]& ]], Times @@ # == n & ]]; Table[a[n], {n, 1, 80}]

A114592aux(n, k) = if(1==n, 1, sumdiv(n, d, if(d > 1 && d <= k && d < n, (-1)*A114592aux(n/d, d-1))) - (n<=k)); \\ After code in A045778.
A114592(n) = A114592aux(n,n);
A114591(n) = sumdiv(n,d,A114592(d)); \\ Antti Karttunen, Jul 23 2017

a(1) = 1; for n>= 2, a(n) = sum, over ways to factor n into any number of distinct composites, of (-1)^(number of composites in a factorization). (See example.)

More terms from Jean-François Alcover, Sep 26 2013

A167746 Number of prime divisors of A001222 (counted with multiplicity), with a(1) = 1 by convention.

Original entry on oeis.org

1, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 2, 0, 1, 0, 1, 1, 1, 0, 2, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 2, 0, 1, 1, 2, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 2, 1, 2, 1, 1, 0, 2, 0, 1, 1, 2, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 2, 1, 0, 2, 1, 1, 1, 2, 0, 2, 1, 1, 1, 1, 1, 2, 0, 1, 1, 2, 0, 1, 0, 2, 1

Offset: 1

Vladimir Joseph Stephan Orlovsky, Nov 10 2009

nonn

First 31 terms the same as A050370.

Antti Karttunen, Table of n, a(n) for n = 1..10000
Index entries for sequences computed from exponents in factorization of n

Cf. A001222.

Array[If[# == 1, 1, Nest[PrimeOmega, #, 2]] &, 105] (* Michael De Vlieger, Jul 29 2017 *)

a(n) = if (n==1, 1, bigomega(bigomega(n))); \\ Michel Marcus, Jul 28 2017

(define (A167746 n) (if (= 1 n) 1 (A001222 (A001222 n)))) ;; Antti Karttunen, Jul 28 2017

a(1) = 1; for n > 1, a(n) = A001222(A001222(n)). - Antti Karttunen, Jul 28 2017

Name clarified by Antti Karttunen, Jul 28 2017

A376679 Number of strict integer factorizations of n into nonsquarefree factors > 1.

Original entry on oeis.org

1, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 2, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 1, 2, 0, 0, 0, 1, 0, 0, 0, 3, 0, 0, 1, 1, 0, 0, 0, 2, 1, 0, 0, 1, 0, 0, 0

Offset: 1

Gus Wiseman, Oct 08 2024

nonn

			The a(3456) = 28 factorizations are:
  (4*8*9*12)  (4*9*96)    (36*96)   (3456)
              (8*9*48)    (4*864)
              (4*12*72)   (48*72)
              (4*16*54)   (54*64)
              (4*18*48)   (8*432)
              (4*24*36)   (9*384)
              (4*27*32)   (12*288)
              (4*8*108)   (16*216)
              (8*12*36)   (18*192)
              (8*16*27)   (24*144)
              (8*18*24)   (27*128)
              (9*12*32)   (32*108)
              (9*16*24)
              (12*16*18)

Dominic McCarty, Table of n, a(n) for n = 1..10000

Positions of zeros are A005117 (squarefree numbers), complement A013929.
For squarefree instead of nonsquarefree we have A050326, non-strict A050320.
For prime-powers we have A050361, non-strict A000688.
For nonprime numbers we have A050372, non-strict A050370.
The version for partitions is A256012, non-strict A114374.
For perfect-powers we have A323090, non-strict A294068.
The non-strict version is A376657.
Nonsquarefree numbers:
- A078147 (first differences)
- A376593 (second differences)
- A376594 (inflections and undulations)
- A376595 (nonzero curvature)
A000040 lists the prime numbers, differences A001223.
A001055 counts integer factorizations, strict A045778.
A005117 lists squarefree numbers, differences A076259.
A317829 counts factorizations of superprimorials, strict A337069.
Cf. A008480, A053797, A053806, A061398, A089259, A120992, A303707, A322452, A375707, A376312.

function nextNonSquareFree(val){val+=1;for(let i=2;i*i<=val;i+=1){if(val%i==0&&val%(i*i)==0){return val}}return nextNonSquareFree(val)}function strictFactorCount(val,maxFactor){if(val==1){return 1}let sum=0;while(maxFactorDominic McCarty, Oct 19 2024

facs[n_]:=If[n<=1,{{}},Join@@Table[Map[Prepend[#,d]&,Select[facs[n/d],Min@@#>=d&]],{d,Rest[Divisors[n]]}]];
Table[Length[Select[facs[n],UnsameQ@@#&&NoneTrue[#,SquareFreeQ]&]],{n,100}] (* corrected by Gus Wiseman, Jun 27 2025 *)

A376657 Number of integer factorizations of n into nonsquarefree factors > 1.

Original entry on oeis.org

1, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 2, 0, 1, 0, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 2, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 1, 4, 0, 0, 0, 1, 0, 0, 0, 3, 0, 0, 1, 1, 0, 0, 0, 2, 2, 0, 0, 1, 0, 0, 0

Offset: 1

Gus Wiseman, Oct 07 2024

nonn

			The a(n) factorizations for n = 16, 64, 72, 144, 192, 256, 288:
  (16)   (64)     (72)    (144)    (192)     (256)      (288)
  (4*4)  (8*8)    (8*9)   (4*36)   (4*48)    (4*64)     (4*72)
         (4*16)   (4*18)  (8*18)   (8*24)    (8*32)     (8*36)
         (4*4*4)          (9*16)   (12*16)   (16*16)    (9*32)
                          (12*12)  (4*4*12)  (4*8*8)    (12*24)
                          (4*4*9)            (4*4*16)   (16*18)
                                             (4*4*4*4)  (4*8*9)
                                                        (4*4*18)

For prime-powers we have A000688.
Positions of zeros are A005117 (squarefree numbers), complement A013929.
For squarefree instead of nonsquarefree we have A050320, strict A050326.
For nonprime numbers we have A050370.
The version for partitions is A114374.
For perfect-powers we have A294068.
For non-perfect-powers we have A303707.
For non-prime-powers we have A322452.
The strict case is A376679.
Nonsquarefree numbers:
- A078147 (first differences)
- A376593 (second differences)
- A376594 (inflections and undulations)
- A376595 (nonzero curvature)
A000040 lists the prime numbers, differences A001223.
A001055 counts integer factorizations, strict A045778.
A005117 lists squarefree numbers, differences A076259.
A317829 counts factorizations of superprimorials, strict A337069.
Cf. A008480, A053797, A053806, A061398, A089259, A120992, A124010, A182853, A373198, A375707, A376312.

facs[n_]:=If[n<=1,{{}},Join@@Table[Map[Prepend[#,d]&,Select[facs[n/d],Min@@#>=d&]],{d,Rest[Divisors[n]]}]];
Table[Length[Select[facs[n],NoneTrue[SquareFreeQ]]],{n,100}]

A349223 Numbers k with a record number of ways to factor k into composite factors.

Original entry on oeis.org

1, 4, 16, 36, 64, 96, 144, 240, 288, 360, 432, 480, 576, 720, 864, 960, 1152, 1440, 2160, 2880, 4320, 5040, 5760, 7200, 8640, 10080, 11520, 12960, 14400, 15120, 17280, 20160, 25920, 28800, 30240, 34560, 40320, 50400, 51840, 60480, 80640, 86400, 90720, 100800, 120960

Offset: 1

Amiram Eldar, Nov 11 2021

nonn

Except for the term 4, the indices of records of A050370.

The corresponding record values are 0, 1, 2, 3, 4, 5, 8, 9, 11, 12, 13, 14, ... (see the link for more values).

			a(1) = 1 since 1 has 0 ways to be factored into composite factors.
a(2) = 4 since 4 is composite and has 1 presentation as a product of composite numbers: 4.
a(3) = 16 since 16 has 2 presentations as a product of composite numbers: 4 * 4 and 16.
a(4) = 36 since 36 has 3 presentations as a product of composite numbers: 6 * 6, 4 * 9 and 36.

Amiram Eldar, Table of n, a(n) for n = 1..200
Amiram Eldar, Table of n, a(n) and record values for n = 1..200

Cf. A002808, A050370.

Subsequence of A025487.

f[, 1] = f[1, ] = 1; f[n_, m_] := f[n, m] = DivisorSum[n, f[n/#, #] &, 1 < # <= m &]; g[n_] := DivisorSum[n, MoebiusMu[n/#]*f[#, #] &]; gm = 0; seq = {1}; Do[g1 = g[n]; If[g1 > gm, gm = g1; AppendTo[seq, n]], {n, 2, 10^5}]; seq

cp's OEIS Frontend

A114591 A composite analog of the Moebius function: Sum_{n>=1} a(n)/n^s = Product_{c=composites} (1 - 1/c^s) = zeta(s) *Product_{k>=2} (1 - 1/k^s).

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A167746 Number of prime divisors of A001222 (counted with multiplicity), with a(1) = 1 by convention.

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A376679 Number of strict integer factorizations of n into nonsquarefree factors > 1.

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A376657 Number of integer factorizations of n into nonsquarefree factors > 1.

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A349223 Numbers k with a record number of ways to factor k into composite factors.

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