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.

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A331378 Numbers whose product of prime indices is divisible by their sum of prime factors.

Original entry on oeis.org

35, 65, 95, 98, 154, 189, 297, 324, 363, 364, 375, 450, 476, 585, 623, 702, 763, 765, 791, 812, 826, 918, 938, 994, 1036, 1064, 1106, 1144, 1148, 1162, 1197, 1225, 1287, 1288, 1300, 1305, 1309, 1449, 1470, 1484, 1517, 1566, 1593, 1665, 1708, 1710, 1736, 1769
Offset: 1

Views

Author

Gus Wiseman, Jan 15 2020

Keywords

Comments

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

Examples

			The sequence of terms together with their prime indices begins:
    35: {3,4}
    65: {3,6}
    95: {3,8}
    98: {1,4,4}
   154: {1,4,5}
   189: {2,2,2,4}
   297: {2,2,2,5}
   324: {1,1,2,2,2,2}
   363: {2,5,5}
   364: {1,1,4,6}
   375: {2,3,3,3}
   450: {1,2,2,3,3}
   476: {1,1,4,7}
   585: {2,2,3,6}
   623: {4,24}
   702: {1,2,2,2,6}
   763: {4,29}
   765: {2,2,3,7}
   791: {4,30}
   812: {1,1,4,10}
For example, 450 = prime(1)*prime(2)*prime(2)*prime(3)*prime(3) has prime indices {1,2,2,3,3} and prime factors {2,3,3,5,5}, and since 36 is divisible by 18, 450 is in the sequence.

Links

Crossrefs

These are the Heinz numbers of the partitions counted by A330954.
Numbers divisible by the sum of their prime factors are A036844.
Numbers divisible by the sum of their prime indices are A324851.
Sum of prime indices divides product of prime indices: A326149.
Partitions whose Heinz number is divisible by their sum are A330950.
Partitions whose product divides their sum of primes are A331381.
Product of prime indices equals sum of prime factors: A331384.
Cf. A000040, A001414, A056239, A057568, A324850, A330953, A331379, A331381, A331382, A331383.

Programs

  • Mathematica
    primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[2,1000],Divisible[Times@@primeMS[#],Total[Prime/@primeMS[#]]]&]

A331384 Numbers whose sum of prime factors is equal to their product of prime indices.

Original entry on oeis.org

35, 65, 95, 98, 154, 324, 364, 476, 623, 763, 791, 812, 826, 938, 994, 1036, 1064, 1106, 1144, 1148, 1162, 1288, 1484, 1708, 1736, 2044, 2408, 2632, 4320, 5408, 6688, 6974, 8000, 10208, 12623, 12701, 12779, 14144, 19624, 23144, 25784, 26048, 44176, 47696
Offset: 1

Views

Author

Gus Wiseman, Jan 16 2020

Keywords

Comments

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.
Numbers k such that A001414(k) = A003963(k). - Jason Yuen, Dec 19 2024

Examples

			The sequence of terms together with their prime indices begins:
     35: {3,4}
     65: {3,6}
     95: {3,8}
     98: {1,4,4}
    154: {1,4,5}
    324: {1,1,2,2,2,2}
    364: {1,1,4,6}
    476: {1,1,4,7}
    623: {4,24}
    763: {4,29}
    791: {4,30}
    812: {1,1,4,10}
    826: {1,4,17}
    938: {1,4,19}
    994: {1,4,20}
   1036: {1,1,4,12}
   1064: {1,1,1,4,8}
   1106: {1,4,22}
   1144: {1,1,1,5,6}
   1148: {1,1,4,13}
For example, 476 has prime factors {2,2,7,17} and prime indices {1,1,4,7}, and 2+2+7+17 = 28 = 1*1*4*7, so 476 is in the sequence.

Crossrefs

These are the Heinz numbers of the partitions counted by A331383.
Numbers divisible by the sum of their prime factors are A036844.
Partitions whose product is divisible by their sum are A057568.
Numbers divisible by the sum of their prime indices are A324851.
Product of prime indices is divisible by sum of prime indices: A326149.
Partitions whose Heinz number is divisible by their sum are A330950.
Partitions whose Heinz number is divisible by their sum of primes: A330953.
Sum of prime factors is divisible by sum of prime indices: A331380
Partitions whose product divides their sum of primes are A331381.
Cf. A000040, A001414, A003963, A324850, A330954, A331378, A331379, A331382, A331415, A331416.

Programs

  • Mathematica
    primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[1000],Times@@primeMS[#]==Plus@@Prime/@primeMS[#]&]

A159578 Dividend associated with A116536.

Original entry on oeis.org

2, 30, 9699690, 304250263527210, 267064515689275851355624017992790, 5766152219975951659023630035336134306565384015606066319856068810, 962947420735983927056946215901134429196419130606213075415963491270, 29819592777931214269172453467810429868925511217482600306406141434158090
Offset: 1

Views

Author

Enoch Haga, Apr 16 2009

Keywords

Comments

a(2)-a(4) are mentioned by Alladi and Erdős (1977). They conjectured that this sequence is infinite. - Amiram Eldar, Nov 02 2020

Examples

			a(2) = 30 because 2*3*5 = 30, 2+3+5 = 10, and 30/10 = 3 in A116536.

Links

Crossrefs

Intersection of A002110 and A036844.
Cf. A051838, A116536.

Programs

  • Maple
    # First define t1, the sequence A051838.
t1:=[1,3,8,13,23,38,39,41,43,48,50,53,56,57,58,66,68,
70,73,77,84,90,94,98,126,128,134,140,143,145,149,
151,153,157,160,164,167,168,172,174,176,182,191,
194,196,200,210,212,215,217,218,219,222,225,228,
229];
p:=ithprime;
num:=n->mul(p(i),i=1..t1[n]);
s:=[num(i),i=1..11)];
  • Mathematica
    seq = {}; sum = 0; prod = 1; p = 1; Do[p = NextPrime[p]; prod *= p; sum += p; If[Divisible[prod, sum], AppendTo[seq, prod]], {50}]; seq (* Amiram Eldar, Nov 02 2020 *)
Module[{nn=50,s,p},s=Accumulate[Prime[Range[nn]]];p=FoldList[Times,Prime[Range[ nn]]]; Select[Thread[{p,s}],Divisible[#[[1]],#[[2]]]&]][[All,1]] (* Harvey P. Dale, Jun 07 2022 *)

Formula

a(n) = A002110(A051838(n)). - Amiram Eldar, Nov 02 2020

Extensions

Corrected by N. J. A. Sloane, Oct 02 2011 (all the terms were wrong).

A331415 Sum of prime factors minus sum of prime indices of n.

Original entry on oeis.org

0, 1, 1, 2, 2, 2, 3, 3, 2, 3, 6, 3, 7, 4, 3, 4, 10, 3, 11, 4, 4, 7, 14, 4, 4, 8, 3, 5, 19, 4, 20, 5, 7, 11, 5, 4, 25, 12, 8, 5, 28, 5, 29, 8, 4, 15, 32, 5, 6, 5, 11, 9, 37, 4, 8, 6, 12, 20, 42, 5, 43, 21, 5, 6, 9, 8, 48, 12, 15, 6, 51, 5, 52, 26, 5, 13, 9, 9
Offset: 1

Views

Author

Gus Wiseman, Jan 17 2020

Keywords

Comments

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

Examples

			The prime factors of 12 are {2,2,3}, while the prime indices are {1,1,2}, so a(12) = 7 - 4 = 3.

Crossrefs

The number of k's is A331387(k) = sum of k-th column of A331385.
The sum of prime factors of n is A001414(n).
The sum of prime indices of n is A056239(n).
Numbers divisible by the sum of their prime factors are A036844.
Sum of prime factors is divisible by sum of prime indices: A331380
Product of prime indices equals sum of prime factors: A331384.
Cf. A000040, A000720, A001222, A014689, A056239, A112798, A301987, A318995, A325036, A330953, A331378, A331379, A331416, A331418.

Programs

  • Mathematica
    Table[Total[Cases[If[n==1,{},FactorInteger[n]],{p_,k_}:>k*(p-PrimePi[p])]],{n,30}]

Formula

Totally additive with a(prime(k)) = prime(k) - k = A014689(k).
a(n) = A001414(n) - A056239(n).

A238525 n modulo sopfr(n), where sopfr(n) is the sum of the prime factors of n, with multiplicity.

Original entry on oeis.org

0, 0, 0, 0, 1, 0, 2, 3, 3, 0, 5, 0, 5, 7, 0, 0, 2, 0, 2, 1, 9, 0, 6, 5, 11, 0, 6, 0, 0, 0, 2, 5, 15, 11, 6, 0, 17, 7, 7, 0, 6, 0, 14, 1, 21, 0, 4, 7, 2, 11, 1, 0, 10, 7, 4, 13, 27, 0, 0, 0, 29, 11, 4, 11, 2, 0, 5, 17, 0, 0, 0, 0, 35, 10, 7, 5, 6, 0, 2, 9, 39
Offset: 2

Views

Author

J. Stauduhar, Feb 28 2014

Keywords

Comments

a(A036844(n)) = 0. - Reinhard Zumkeller, Jul 21 2014

Examples

			a(6) = 1, because 6 mod sopfr(6) = 6 mod 5 = 1.

Links

Crossrefs

Cf. A001414, A238526, A238527, A238528, A238529, A238530.
Cf. A036844.

Programs

  • Haskell
    a238525 n = mod n $ a001414 n  -- Reinhard Zumkeller, Jul 21 2014
  • Mathematica
    Table[Mod[n, Apply[Dot, Transpose[FactorInteger[n]]]], {n, 105}] (* Wouter Meeussen, Mar 01 2014 *)
mms[n_]:=Mod[n,Total[Flatten[Table[#[[1]],#[[2]]]&/@FactorInteger[ n]]]]; Array[mms,90,2] (* Harvey P. Dale, May 25 2016 *)

Formula

a(n) = n mod A001414(n).

A331380 Numbers whose sum of prime factors is divisible by their sum of prime indices.

Original entry on oeis.org

2, 4, 8, 16, 32, 33, 39, 55, 64, 65, 66, 74, 77, 78, 86, 91, 110, 128, 130, 132, 154, 156, 164, 182, 188, 220, 256, 260, 264, 308, 312, 364, 371, 411, 440, 459, 512, 513, 520, 528, 530, 616, 624, 636, 689, 728, 746, 755, 765, 766, 855, 880, 906, 915, 918, 1007
Offset: 1

Views

Author

Gus Wiseman, Jan 16 2020

Keywords

Comments

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

Examples

			The sequence of terms together with their prime indices begins:
     2: {1}
     4: {1,1}
     8: {1,1,1}
    16: {1,1,1,1}
    32: {1,1,1,1,1}
    33: {2,5}
    39: {2,6}
    55: {3,5}
    64: {1,1,1,1,1,1}
    65: {3,6}
    66: {1,2,5}
    74: {1,12}
    77: {4,5}
    78: {1,2,6}
    86: {1,14}
    91: {4,6}
   110: {1,3,5}
   128: {1,1,1,1,1,1,1}
   130: {1,3,6}
   132: {1,1,2,5}
For example, 132 has prime factors {2,2,3,11} and prime indices {1,1,2,5}, and 18 is divisible by 9, so 132 is in the sequence.

Crossrefs

These are the Heinz numbers of the partitions counted by A331380.
Numbers divisible by the sum of their prime factors are A036844.
Partitions whose product is divisible by their sum are A057568.
Numbers divisible by the sum of their prime indices are A324851.
Product of prime indices is divisible by sum of prime indices: A326149.
Partitions whose Heinz number is divisible by their sum are A330950.
Heinz number is divisible by sum of primes: A330953.
Partitions whose product divides their sum of primes are A331381.
Partitions whose product is equal to their sum of primes are A331383.
Product of prime indices equals sum of prime factors: A331384.
Cf. A000040, A001414, A056239, A330954, A331378, A331379, A331382, A331415, A331416.

Programs

  • Mathematica
    primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[2,100],Divisible[Plus@@Prime/@primeMS[#],Plus@@primeMS[#]]&]

A331382 Numbers whose sum of prime factors is divisible by their product of prime indices.

Original entry on oeis.org

1, 2, 4, 8, 16, 18, 20, 32, 35, 44, 60, 62, 64, 65, 68, 72, 92, 95, 98, 128, 154, 160, 168, 256, 264, 288, 291, 303, 324, 364, 400, 476, 480, 512, 618, 623, 624, 642, 706, 763, 791, 812, 816, 826, 938, 994, 1024, 1036, 1064, 1068, 1106, 1144, 1148, 1152, 1162
Offset: 1

Views

Author

Gus Wiseman, Jan 16 2020

Keywords

Comments

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

Examples

			The sequence of terms together with their prime indices begins:
     1: {}
     2: {1}
     4: {1,1}
     8: {1,1,1}
    16: {1,1,1,1}
    18: {1,2,2}
    20: {1,1,3}
    32: {1,1,1,1,1}
    35: {3,4}
    44: {1,1,5}
    60: {1,1,2,3}
    62: {1,11}
    64: {1,1,1,1,1,1}
    65: {3,6}
    68: {1,1,7}
    72: {1,1,1,2,2}
    92: {1,1,9}
    95: {3,8}
    98: {1,4,4}
   128: {1,1,1,1,1,1,1}
For example, 60 has prime factors {2,2,3,5} and prime indices {1,1,2,3}, and 12 is divisible by 6, so 60 is in the sequence.

Crossrefs

These are the Heinz numbers of the partitions counted by A331381.
Numbers divisible by the sum of their prime factors are A036844.
Partitions whose product is divisible by their sum are A057568.
Numbers divisible by the sum of their prime indices are A324851.
Product of prime indices is divisible by sum of prime indices: A326149.
Partitions whose Heinz number is divisible by their sum are A330950.
Sum of prime factors is divisible by sum of prime indices: A331380
Partitions whose product is equal to the sum of primes are A331383.
Product of prime indices equals sum of prime factors: A331384.
Cf. A000040, A001414, A324850, A330953, A330954, A331378, A331379.

Programs

  • Mathematica
    primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[100],Divisible[Plus@@Prime/@primeMS[#],Times@@primeMS[#]]&]

A379320 Number of integer partitions of n whose product is a multiple of n + 1.

Original entry on oeis.org

1, 0, 0, 0, 0, 1, 0, 2, 2, 3, 0, 14, 0, 7, 15, 53, 0, 81, 0, 110, 61, 32, 0, 562, 170, 62, 621, 560, 0, 1400, 0, 3387, 569, 199, 1515, 7734, 0, 339, 1486, 13374, 0, 11926, 0, 8033, 27164, 913, 0, 85326, 15947, 47588, 8294, 25430, 0, 174779, 39748, 169009
Offset: 0

Views

Author

Gus Wiseman, Jan 18 2025

Keywords

Comments

Also the number of integer partitions of n containing 1 whose product is a multiple of n. Without requiring a 1 we get A057568.

Examples

			The a(5) = 1 through a(11) = 14 partitions:
  (3,2)  .  (4,2,1)    (3,3,2)    (5,4)      .  (8,3)
            (2,2,2,1)  (3,3,1,1)  (5,2,2)       (4,4,3)
                                  (5,2,1,1)     (6,3,2)
                                                (6,4,1)
                                                (4,3,2,2)
                                                (4,3,3,1)
                                                (6,2,2,1)
                                                (3,2,2,2,2)
                                                (3,3,2,2,1)
                                                (4,3,2,1,1)
                                                (6,2,1,1,1)
                                                (3,2,2,2,1,1)
                                                (4,3,1,1,1,1)
                                                (3,2,2,1,1,1,1)

Crossrefs

For n instead of n+1 we have A057568 (strict A379733), ranks A326149.
These partitions are ranked by A380217 = A379319/2 = (even case of A326149)/2.
The case of equality is A380218, see also A028422 = A001055 - 1 (ranks A325041).
A000041 counts integer partitions, strict A000009.
A379666 counts partitions by sum and product.
A380219 counts partitions of n whose product is a proper multiple of n, ranks A380216.
Counting and ranking multisets by comparing sum and product:
- same: A001055, ranks A301987
- multiple: A057567, ranks A326155
- divisor: A057568, ranks A326149
- greater than: A096276 shifted right, ranks A325038
- greater or equal: A096276, ranks A325044
- less than: A114324, ranks A325037, see A318029, A379720
- less or equal: A319005, ranks A379721, see A025147
- different: A379736, ranks A379722, see A111133
Cf. A003963, A036844, A069016, A318950, A319000, A319916, A324851, A325042, A326150, A326152, A326156, A379671, A379678, A379734.

Programs

  • Mathematica
    Table[Length[Select[IntegerPartitions[n],Divisible[Times@@#,n+1]&]],{n,0,30}]
  • PARI
    a(n) = my(nb=0); forpart(p=n, if (!(vecprod(Vec(p)) % (n+1)), nb++)); nb; \\ Michel Marcus, Jan 21 2025

A379844 Squarefree numbers x such that the product of prime indices of x is a multiple of the sum of prime indices of x.

Original entry on oeis.org

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 30, 31, 37, 41, 43, 47, 53, 59, 61, 65, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 154, 157, 163, 165, 167, 173, 179, 181, 190, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241
Offset: 1

Views

Author

Gus Wiseman, Jan 19 2025

Keywords

Comments

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798. The sum and product of prime indices are A056239 and A003963 respectively.

Crossrefs

Squarefree case of A326149.
For nonprime instead of squarefree we have A326150.
The non-prime case is A326158.
Partitions of this type are counted by A379733, see A379735.
The even case is A379845, counted by A380221.
A003963 multiplies together prime indices.
A005117 lists the squarefree numbers.
A056239 adds up prime indices.
Counting and ranking multisets by comparing sum and product:
- same: A001055, ranks A301987
- divisible: A057567, ranks A326155
- divisor: A057568, ranks A326149
- greater than: A096276 shifted right, ranks A325038
- greater or equal: A096276, ranks A325044
- less than: A114324, ranks A325037, see A318029, A379720
- less or equal: A319005, ranks A379721, see A025147
- different: A379736, ranks A379722, see A111133
Cf. A000720, A001222, A036844, A112798, A324850, A324851, A324925, A326151, A326153/A326154, A326156, A326157.

Programs

  • Mathematica
    prix[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[2,100],SquareFreeQ[#]&&Divisible[Times@@prix[#],Plus@@prix[#]]&]

Formula

Satisfies A056239(a(n))|A003963(a(n)).

A380216 Numbers whose prime indices have (product)/(sum) equal to an integer > 1.

Original entry on oeis.org

49, 63, 65, 81, 125, 150, 154, 165, 169, 190, 198, 259, 273, 333, 351, 361, 364, 385, 390, 435, 442, 468, 481, 490, 495, 506, 525, 561, 580, 595, 609, 630, 658, 675, 700, 714, 741, 765, 781, 783, 810, 840, 841, 846, 874, 900, 918, 925, 931, 935, 952, 988
Offset: 1

Views

Author

Gus Wiseman, Jan 23 2025

Keywords

Comments

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798. The sum and product of prime indices are A056239 and A003963 respectively.

Examples

			The terms together with their prime indices begin:
   49: {4,4}
   63: {2,2,4}
   65: {3,6}
   81: {2,2,2,2}
  125: {3,3,3}
  150: {1,2,3,3}
  154: {1,4,5}
  165: {2,3,5}
  169: {6,6}
  190: {1,3,8}
  198: {1,2,2,5}
  259: {4,12}
  273: {2,4,6}
  333: {2,2,12}
  351: {2,2,2,6}
  361: {8,8}
  364: {1,1,4,6}
For example, 198 has prime indices {1,2,2,5}, and 20/10 is an integer > 1, so 198 is in the sequence.

Crossrefs

The fraction A003963(n)/A056239(n) reduces to A326153(n)/A326154(n).
The non-proper version is A326149, superset of A326150.
Also a superset of A326151.
The squarefree case is A326158 without first term.
Partitions of this type are counted by A380219.
A379666 counts partitions by sum and product.
Counting and ranking multisets by comparing sum and product:
- same: A001055, ranks A301987
- multiple: A057567, ranks A326155
- divisor: A057568 (strict A379733), ranks A326149, see A379735, A380217.
- greater than: A096276 shifted right, ranks A325038
- greater or equal: A096276, ranks A325044
- less than: A114324, ranks A325037, see A318029, A379720
- less or equal: A319005, ranks A379721, see A025147
- different: A379736, ranks A379722, see A111133
Cf. A000720, A001222, A028422, A036844, A112798, A301988, A319000, A324850, A324851, A326156, A379319, A379844.

Programs

  • Mathematica
    prix[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[2,1000],Divisible[Times@@prix[#],Total[prix[#]]]&&!SameQ[Times@@prix[#],Total[prix[#]]]&]
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