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 14 results. Next

A326149 Numbers whose product of prime indices is divisible by their sum of prime indices.

Original entry on oeis.org

2, 3, 5, 7, 9, 11, 13, 17, 19, 23, 29, 30, 31, 37, 41, 43, 47, 49, 53, 59, 61, 63, 65, 67, 71, 73, 79, 81, 83, 84, 89, 97, 101, 103, 107, 108, 109, 113, 125, 127, 131, 137, 139, 149, 150, 151, 154, 157, 163, 165, 167, 169, 173, 179, 181, 190, 191, 193, 197
Offset: 1

Views

Author

Gus Wiseman, Jun 09 2019

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 Heinz number of an integer partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k), so these are Heinz numbers of integer partitions whose product of parts is divisible by their sum of parts. The enumeration of these partitions by sum is given by A057568.

Examples

			The sequence of terms together with their prime indices begins:
    2: {1}
    3: {2}
    5: {3}
    7: {4}
    9: {2,2}
   11: {5}
   13: {6}
   17: {7}
   19: {8}
   23: {9}
   29: {10}
   30: {1,2,3}
   31: {11}
   37: {12}
   41: {13}
   43: {14}
   47: {15}
   49: {4,4}
   53: {16}
   59: {17}

Links

Crossrefs

Satisfies A056239(a(n))|A003963(a(n)).
The nonprime case is A326150, with squarefree case A326158.
Cf. A000720, A001222, A057567, A057568, A112798, A301987.
Cf. A325037, A325042, A325044, A326151, A326153/A326154, A326155, A326156.

Programs

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

A326155 Positive integers whose sum of prime indices is divisible by their product of prime indices.

Original entry on oeis.org

1, 2, 3, 4, 5, 7, 8, 9, 11, 12, 13, 16, 17, 19, 23, 29, 30, 31, 32, 37, 40, 41, 43, 47, 48, 53, 59, 61, 64, 67, 71, 73, 79, 83, 84, 89, 97, 101, 103, 107, 108, 109, 112, 113, 127, 128, 131, 137, 139, 144, 149, 151, 157, 163, 167, 173, 179, 181, 191, 192, 193
Offset: 1

Views

Author

Gus Wiseman, Jun 10 2019

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.
Also Heinz numbers of the integer partitions counted by A057567. The Heinz number of an integer partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k).

Examples

			The sequence of terms together with their prime indices begins:
   1: {}
   2: {1}
   3: {2}
   4: {1,1}
   5: {3}
   7: {4}
   8: {1,1,1}
   9: {2,2}
  11: {5}
  12: {1,1,2}
  13: {6}
  16: {1,1,1,1}
  17: {7}
  19: {8}
  23: {9}
  29: {10}
  30: {1,2,3}
  31: {11}
  32: {1,1,1,1,1}
  37: {12}

Links

Crossrefs

One and positions of ones in A326153.
Cf. A003963, A056239, A057567, A057568, A112798, A301987.
Cf. A325037, A325042, A325044, A326150, A326151, A326154, A326156, A326158.

Programs

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

A326152 Number of integer partitions of n whose product of parts is 2 * n.

Original entry on oeis.org

0, 0, 0, 0, 0, 0, 0, 0, 3, 2, 2, 0, 5, 0, 2, 3, 5, 0, 7, 0, 5, 3, 2, 0, 10, 2, 2, 5, 5, 0, 9, 0, 9, 3, 2, 3, 14, 0, 2, 3, 10, 0, 9, 0, 5, 9, 2, 0, 17, 2, 7, 3, 5, 0, 14, 3, 10, 3, 2, 0, 19, 0, 2, 9, 13, 3, 9, 0, 5, 3, 9, 0, 27, 0, 2, 9, 5, 3, 9, 0, 17, 10, 2, 0
Offset: 0

Views

Author

Gus Wiseman, Jun 09 2019

Keywords

Comments

Also the number of orderless factorizations of 2 * n into factors > 1 with sum at most n.
The Heinz numbers of these partitions are given by A326151.

Examples

			The a(8) = 3 through a(16) = 5 partitions (empty columns not shown) (A = 10):
  (44)    (63)    (541)   (831)      (74111)   (A311)      (841111)
  (422)   (3321)  (5221)  (6411)     (722111)  (651111)    (8221111)
  (2222)                  (62211)              (53211111)  (442111111)
                          (432111)                         (4222111111)
                          (3222111)                        (22222111111)

Crossrefs

Cf. A003963, A057567, A057568, A096276, A114324, A301987, A319005, A326149, A326151, A326156, A326157.

Programs

  • Mathematica
    Table[Length[Select[IntegerPartitions[n],Times@@#==2*n&]],{n,0,30}]

A326156 Number of nonempty subsets of {1..n} whose product is divisible by their sum.

Original entry on oeis.org

0, 1, 2, 4, 5, 10, 19, 34, 64, 129, 267, 541, 1104, 2253, 4694, 9804, 18894, 38539, 76063, 155241, 311938, 636120, 1299869, 2653853, 5183363, 10272289, 20958448, 40945577, 81745769, 167048919, 329598054, 671038751, 1301431524, 2618590422, 5305742557, 10582105199, 20660489585, 42075929255, 85443680451, 172057673225, 338513788818
Offset: 0

Views

Author

Gus Wiseman, Jun 11 2019

Keywords

Examples

			The a(1) = 1 through a(6) = 19 subsets:
  {1}  {1}  {1}      {1}      {1}          {1}
       {2}  {2}      {2}      {2}          {2}
            {3}      {3}      {3}          {3}
            {1,2,3}  {4}      {4}          {4}
                     {1,2,3}  {5}          {5}
                              {1,2,3}      {6}
                              {1,4,5}      {3,6}
                              {2,3,5}      {1,2,3}
                              {3,4,5}      {1,4,5}
                              {1,2,3,4,5}  {2,3,5}
                                           {2,4,6}
                                           {3,4,5}
                                           {4,5,6}
                                           {1,2,3,6}
                                           {1,3,5,6}
                                           {3,4,5,6}
                                           {1,2,3,4,5}
                                           {1,2,3,4,6}
                                           {2,3,4,5,6}

Links

Crossrefs

Cf. A053632, A057567, A057568, A059529, A063865, A301987, A326150, A326151, A326153/A326154, A326155, A326158, A326178, A326179, A326180.

Programs

  • Mathematica
    Table[Length[Select[Subsets[Range[n],{1,n}],Divisible[Times@@#,Plus@@#]&]],{n,0,10}]

Extensions

a(21)-a(30) from Alois P. Heinz, Jun 13 2019
a(31)-a(40) from Bert Dobbelaere, Jun 22 2019

A326153 Numerator of the product of prime indices of n divided by the sum of prime indices of n, n > 1.

Original entry on oeis.org

1, 1, 1, 1, 2, 1, 1, 1, 3, 1, 1, 1, 4, 6, 1, 1, 4, 1, 3, 4, 5, 1, 2, 3, 6, 4, 2, 1, 1, 1, 1, 10, 7, 12, 2, 1, 8, 3, 1, 1, 8, 1, 5, 12, 9, 1, 1, 2, 9, 14, 3, 1, 8, 15, 4, 8, 10, 1, 6, 1, 11, 2, 1, 2, 5, 1, 7, 18, 3, 1, 4, 1, 12, 9, 4, 20, 4, 1, 3, 2, 13, 1, 1
Offset: 2

Views

Author

Gus Wiseman, Jun 09 2019

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 A326153/A326154 begins: 1, 1, 1/2, 1, 2/3, 1, 1/3, 1, 3/4, 1, 1/2, 1, 4/5, 6/5, 1/4, 1, 4/5, 1, 3/5, 4/3, 5/6, 1, 2/5, 3/2, 6/7, 4/3.

Crossrefs

Numerator of A003963(n)/A056239(n).
Positions of ones are A326155 without the first term.
Cf. A057567, A057568, A112798, A301987, A325037, A325042, A325044, A326149, A326150, A326151, A326154, A326156, A326158.

Programs

  • Mathematica
    primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Table[Numerator[Times@@primeMS[n]/Plus@@primeMS[n]],{n,2,100}]

A326154 Denominator of the product of prime indices of n divided by the sum of prime indices of n, n > 1.

Original entry on oeis.org

1, 1, 2, 1, 3, 1, 3, 1, 4, 1, 2, 1, 5, 5, 4, 1, 5, 1, 5, 3, 6, 1, 5, 2, 7, 3, 3, 1, 1, 1, 5, 7, 8, 7, 3, 1, 9, 2, 2, 1, 7, 1, 7, 7, 10, 1, 3, 1, 7, 9, 4, 1, 7, 8, 7, 5, 11, 1, 7, 1, 12, 1, 6, 1, 4, 1, 9, 11, 2, 1, 7, 1, 13, 4, 5, 9, 3, 1, 7, 1, 14, 1, 1, 10
Offset: 2

Views

Author

Gus Wiseman, Jun 09 2019

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 A326153/A326154 begins: 1, 1, 1/2, 1, 2/3, 1, 1/3, 1, 3/4, 1, 1/2, 1, 4/5, 6/5, 1/4, 1, 4/5, 1, 3/5, 4/3, 5/6, 1, 2/5, 3/2, 6/7, 4/3.

Crossrefs

Denominator of A003963(n)/A056239(n).
Positions of ones are A326149.
Cf. A057567, A057568, A112798, A301987, A325037, A325042, A325044, A326150, A326151, A326153, A326155, A326156, A326158.

Programs

  • Mathematica
    primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Table[Denominator[Times@@primeMS[n]/Plus@@primeMS[n]],{n,2,100}]

A326150 Nonprime numbers whose product of prime indices is divisible by their sum of prime indices.

Original entry on oeis.org

9, 30, 49, 63, 65, 81, 84, 108, 125, 150, 154, 165, 169, 190, 198, 200, 259, 264, 273, 333, 351, 361, 364, 385, 390, 435, 442, 468, 481, 490, 495, 506, 525, 561, 580, 595, 609, 624, 630, 658, 675, 700, 714, 741, 765, 781, 783, 810, 840, 841, 846, 874, 900, 918
Offset: 1

Views

Author

Gus Wiseman, Jun 09 2019

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:
    9: {2,2}
   30: {1,2,3}
   49: {4,4}
   63: {2,2,4}
   65: {3,6}
   81: {2,2,2,2}
   84: {1,1,2,4}
  108: {1,1,2,2,2}
  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}
  200: {1,1,1,3,3}
  259: {4,12}
  264: {1,1,1,2,5}
  273: {2,4,6}
  333: {2,2,12}

Crossrefs

Satisfies A056239(a(n))|A003963(a(n)).
The case with primes included is A326149. The squarefree case A326158.
Cf. A057567, A057568, A112798, A301987.
Cf. A325037, A325042, A325044, A326151, A326153/A326154, A326155, A326156.

Programs

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

A326158 Nonprime squarefree numbers whose product of prime indices is divisible by their sum of prime indices.

Original entry on oeis.org

30, 65, 154, 165, 190, 259, 273, 385, 390, 435, 442, 481, 506, 561, 595, 609, 658, 714, 741, 781, 874, 935, 1001, 1110, 1118, 1173, 1254, 1281, 1330, 1363, 1403, 1430, 1455, 1469, 1495, 1505, 1653, 1691, 1771, 1786, 1794, 1798, 1887, 1958, 2035, 2067, 2139
Offset: 1

Views

Author

Gus Wiseman, Jun 10 2019

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:
    30: {1,2,3}
    65: {3,6}
   154: {1,4,5}
   165: {2,3,5}
   190: {1,3,8}
   259: {4,12}
   273: {2,4,6}
   385: {3,4,5}
   390: {1,2,3,6}
   435: {2,3,10}
   442: {1,6,7}
   481: {6,12}
   506: {1,5,9}
   561: {2,5,7}
   595: {3,4,7}
   609: {2,4,10}
   658: {1,4,15}
   714: {1,2,4,7}
   741: {2,6,8}
   781: {5,20}

Links

Crossrefs

Satisfies A056239(a(n))|A003963(a(n)).
The case with squarefree numbers included is A326150.
The case with primes and squarefree numbers included is A326149.
Cf. A057567, A057568, A112798, A301987.
Cf. A325037, A325042, A325044, A326151, A326153/A326154, A326155, A326156.

Programs

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

A326172 Number of nonempty subsets of {2..n} whose product is divisible by their sum.

Original entry on oeis.org

0, 0, 1, 2, 3, 6, 12, 21, 34, 69, 140, 278, 561, 1144, 2367, 4936, 9503, 19368, 38202, 77911, 156458, 318911, 651462, 1329624, 2596458, 5144833, 10494839, 20500025, 40923643, 83620258, 164982516, 335873558, 651383048, 1310551707, 2655240565, 5295397093, 10338145110, 21052407259, 42748787713, 86078893923, 169349494068
Offset: 0

Views

Author

Gus Wiseman, Jun 11 2019

Keywords

Examples

			The a(2) = 1 through a(7) = 21 subsets:
  {2}  {2}  {2}  {2}      {2}          {2}
       {3}  {3}  {3}      {3}          {3}
            {4}  {4}      {4}          {4}
                 {5}      {5}          {5}
                 {2,3,5}  {6}          {6}
                 {3,4,5}  {3,6}        {7}
                          {2,3,5}      {3,6}
                          {2,4,6}      {2,3,5}
                          {3,4,5}      {2,4,6}
                          {4,5,6}      {2,5,7}
                          {3,4,5,6}    {3,4,5}
                          {2,3,4,5,6}  {3,4,7}
                                       {3,5,7}
                                       {4,5,6}
                                       {2,3,6,7}
                                       {2,5,6,7}
                                       {3,4,5,6}
                                       {3,5,6,7}
                                       {2,3,4,5,6}
                                       {2,3,4,5,7}
                                       {2,4,5,6,7}

Crossrefs

Cf. A053632, A057567, A057568, A059529, A063865, A301987, A325037, A325044, A326150, A326151, A326153/A326154, A326155, A326156, A326158, A326178.

Programs

  • Mathematica
    Table[Length[Select[Subsets[Range[2,n],{1,n}],Divisible[Times@@#,Plus@@#]&]],{n,0,10}]

Extensions

a(21)-a(29) from Alois P. Heinz, Jun 13 2019
a(30)-a(40) from Bert Dobbelaere, Jun 22 2019

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)).
Showing 1-10 of 14 results. Next

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