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 1-6 of 6 results.

A322554 Numbers whose product of prime indices is a power of a squarefree number (A072774).

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 36, 38, 40, 41, 42, 43, 44, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 62, 63, 64, 66, 67, 68, 72, 73, 76, 79, 80
Offset: 1

Views

Author

Gus Wiseman, Dec 15 2018

Keywords

Comments

The complement is {35, 37, 39, 45, 61, 65, ...}.
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 multiset multisystem with MM-number n is formed by taking the multiset of prime indices of each part of the multiset of prime indices of n. For example, the prime indices of 78 are {1,2,6}, so the multiset multisystem with MM-number 78 is {{},{1},{1,2}}. This sequence lists all MM-numbers of regular multiset multisystems, where regularity means all vertex-degrees are equal.

Examples

			Most small numbers belong to this sequence. However, the sequence of multiset multisystems whose MM-numbers do not belong to this sequence begins:
  35: {{2},{1,1}}
  37: {{1,1,2}}
  39: {{1},{1,2}}
  45: {{1},{1},{2}}
  61: {{1,2,2}}
  65: {{2},{1,2}}
  69: {{1},{2,2}}
  70: {{},{2},{1,1}}
  71: {{1,1,3}}
  74: {{},{1,1,2}}
  75: {{1},{2},{2}}
  77: {{1,1},{3}}
  78: {{},{1},{1,2}}
  87: {{1},{1,3}}
  89: {{1,1,1,2}}
  90: {{},{1},{1},{2}}
  91: {{1,1},{1,2}}
  95: {{2},{1,1,1}}
  99: {{1},{1},{3}}

Crossrefs

Cf. A003963, A056239, A062503, A072774, A112798, A302242, A302491, A320325, A320698, A322553.

Programs

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

A320699 Numbers whose product of prime indices is a nonprime prime power (A246547).

Original entry on oeis.org

7, 9, 14, 18, 19, 21, 23, 25, 27, 28, 36, 38, 42, 46, 49, 50, 53, 54, 56, 57, 63, 72, 76, 81, 84, 92, 97, 98, 100, 103, 106, 108, 112, 114, 115, 121, 125, 126, 131, 133, 144, 147, 152, 159, 162, 168, 171, 184, 189, 194, 196, 200, 206, 212, 216, 224, 227, 228
Offset: 1

Views

Author

Gus Wiseman, Oct 19 2018

Keywords

Comments

First differs from A320325 at a(43) = 152, A320325(43) = 151.
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 all integer partitions whose Heinz numbers belong to the sequence begins: (4), (2,2), (4,1), (2,2,1), (8), (4,2), (9), (3,3), (2,2,2), (4,1,1), (2,2,1,1), (8,1), (4,2,1), (9,1), (4,4), (3,3,1), (16), (2,2,2,1), (4,1,1,1), (8,2), (4,2,2), (2,2,1,1,1), (8,1,1), (2,2,2,2), (4,2,1,1), (9,1,1), (25), (4,4,1), (3,3,1,1).

Links

Crossrefs

Cf. A000720, A000961, A001597, A003963, A056239, A064573, A112798, A246547, A246655, A279787, A320322, A320325, A320698, A320700.

Programs

  • Mathematica
    Select[Range[100],With[{x=Times@@Cases[FactorInteger[#],{p_,k_}:>PrimePi[p]^k]},!PrimeQ[x]&&PrimePowerQ[x]]&]

A320700 Odd numbers whose product of prime indices is a nonprime prime power (A246547).

Original entry on oeis.org

7, 9, 19, 21, 23, 25, 27, 49, 53, 57, 63, 81, 97, 103, 115, 121, 125, 131, 133, 147, 159, 171, 189, 227, 243, 289, 311, 343, 361, 371, 393, 399, 419, 441, 477, 513, 515, 529, 567, 575, 625, 661, 691, 719, 729, 917, 931, 933, 961, 1007, 1009, 1029, 1067, 1083
Offset: 1

Views

Author

Gus Wiseman, Oct 19 2018

Keywords

Examples

			The sequence of all integer partitions whose Heinz numbers belong to the sequence begins: (4), (2,2), (8), (4,2), (9), (3,3), (2,2,2), (4,4), (16), (8,2), (4,2,2), (2,2,2,2), (25), (27), (9,3), (5,5), (3,3,3), (32), (8,4), (4,4,2), (16,2), (8,2,2), (4,2,2,2), (49), (2,2,2,2,2)

Links

Crossrefs

Cf. A000720, A000961, A001597, A003963, A056239, A064573, A112798, A246547, A279787, A320322, A320325, A320698, A320699.

Programs

  • Mathematica
    Select[Range[1000],With[{x=Times@@Cases[FactorInteger[#],{p_,k_}:>PrimePi[p]^k]},OddQ[#]&&!PrimeQ[x]&&PrimePowerQ[x]]&]

A371290 Numbers whose product of binary indices is a prime power > 1.

Original entry on oeis.org

1, 2, 3, 4, 5, 8, 9, 10, 11, 16, 17, 64, 65, 128, 129, 130, 131, 136, 137, 138, 139, 256, 257, 260, 261, 1024, 1025, 4096, 4097, 32768, 32769, 32770, 32771, 32776, 32777, 32778, 32779, 32896, 32897, 32898, 32899, 32904, 32905, 32906, 32907, 65536, 65537, 262144
Offset: 1

Views

Author

Gus Wiseman, Mar 27 2024

Keywords

Comments

A binary index of n is any position of a 1 in its reversed binary expansion. The binary indices of n are row n of A048793.

Examples

			The terms together with their binary expansions and binary indices begin:
       1:                   1 ~ {1}
       2:                  10 ~ {2}
       3:                  11 ~ {1,2}
       4:                 100 ~ {3}
       5:                 101 ~ {1,3}
       8:                1000 ~ {4}
       9:                1001 ~ {1,4}
      10:                1010 ~ {2,4}
      11:                1011 ~ {1,2,4}
      16:               10000 ~ {5}
      17:               10001 ~ {1,5}
      64:             1000000 ~ {7}
      65:             1000001 ~ {1,7}
     128:            10000000 ~ {8}
     129:            10000001 ~ {1,8}
     130:            10000010 ~ {2,8}
     131:            10000011 ~ {1,2,8}
     136:            10001000 ~ {4,8}
     137:            10001001 ~ {1,4,8}
     138:            10001010 ~ {2,4,8}
     139:            10001011 ~ {1,2,4,8}
     256:           100000000 ~ {9}
     257:           100000001 ~ {1,9}
     260:           100000100 ~ {3,9}
     261:           100000101 ~ {1,3,9}
    1024:         10000000000 ~ {11}
    1025:         10000000001 ~ {1,11}
    4096:       1000000000000 ~ {13}
    4097:       1000000000001 ~ {1,13}
   32768:    1000000000000000 ~ {16}

Crossrefs

For powers of 2 we have A253317.
For prime indices we have A320698.
For squarefree numbers instead of prime powers we have A371289.
A000040 lists prime numbers.
A000961 lists prime-powers.
A048793 lists binary indices, A000120 length, A272020 reverse, A029931 sum.
A070939 gives length of binary expansion.
A096111 gives product of binary indices.
Cf. A005117, A326782, A368533, A371292, A371443, A371452.

Programs

  • Mathematica
    bpe[n_]:=Join@@Position[Reverse[IntegerDigits[n,2]],1];
Select[Range[1000],#==1||PrimePowerQ[Times@@bpe[#]]&]

A322553 Odd numbers whose product of prime indices is a prime power.

Original entry on oeis.org

1, 3, 5, 7, 9, 11, 17, 19, 21, 23, 25, 27, 31, 41, 49, 53, 57, 59, 63, 67, 81, 83, 97, 103, 109, 115, 121, 125, 127, 131, 133, 147, 157, 159, 171, 179, 189, 191, 211, 227, 241, 243, 277, 283, 289, 311, 331, 343, 353, 361, 367, 371, 393, 399, 401, 419, 431, 441
Offset: 1

Views

Author

Gus Wiseman, Dec 15 2018

Keywords

Comments

Differs from A322400 in having 1 and lacking 377, the MM-number of {{1,2},{1,3}}.
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 multiset multisystem with MM-number n is formed by taking the multiset of prime indices of each part of the multiset of prime indices of n. For example, the prime indices of 78 are {1,2,6}, so the multiset multisystem with MM-number 78 is {{},{1},{1,2}}. The sequence of multiset partitions whose MM-numbers belong to this sequence begins:
   1: {}
   3: {{1}}
   5: {{2}}
   7: {{1,1}}
   9: {{1},{1}}
  11: {{3}}
  17: {{4}}
  19: {{1,1,1}}
  21: {{1},{1,1}}
  23: {{2,2}}
  25: {{2},{2}}
  27: {{1},{1},{1}}
  31: {{5}}
  41: {{6}}
  49: {{1,1},{1,1}}
  53: {{1,1,1,1}}
  57: {{1},{1,1,1}}
  59: {{7}}
  63: {{1},{1},{1,1}}
  67: {{8}}
  81: {{1},{1},{1},{1}}
  83: {{9}}
  97: {{3,3}}

Crossrefs

Cf. A003963, A056239, A112798, A290103, A302242, A320325, A320698.

Programs

  • Mathematica
    primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[1,100,2],#==1||PrimePowerQ[Times@@primeMS[#]]&]
  • PARI
    isok(n) = {if (n % 2, my(f = factor(n), pk = prod(k=1, #f~, primepi(f[k,1]))); (pk == 1) || isprimepower(pk););} \\ Michel Marcus, Dec 16 2018

A371287 Numbers whose product of prime indices has exactly two distinct prime factors.

Original entry on oeis.org

13, 15, 26, 29, 30, 33, 35, 37, 39, 43, 45, 47, 51, 52, 55, 58, 60, 61, 65, 66, 69, 70, 71, 73, 74, 75, 77, 78, 79, 85, 86, 87, 89, 90, 91, 93, 94, 95, 99, 101, 102, 104, 105, 107, 110, 111, 116, 117, 119, 120, 122, 123, 129, 130, 132, 135, 137, 138, 139, 140
Offset: 1

Views

Author

Gus Wiseman, Mar 21 2024

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 terms together with their prime indices begin:
  13: {6}
  15: {2,3}
  26: {1,6}
  29: {10}
  30: {1,2,3}
  33: {2,5}
  35: {3,4}
  37: {12}
  39: {2,6}
  43: {14}
  45: {2,2,3}
  47: {15}
  51: {2,7}
  52: {1,1,6}
  55: {3,5}
  58: {1,10}
  60: {1,1,2,3}

Crossrefs

Positions of 2's in A303975 (positions of 1's are A320698).
Counting divisors (not factors) gives A371127, positions of 2's in A370820.
A000005 counts divisors.
A000961 lists powers of primes, of prime index A302596.
A001221 counts distinct prime factors.
A001358 lists semiprimes, squarefree A006881.
A003963 gives product of prime indices.
A027746 lists prime factors, indices A112798, length A001222.
A076610 lists products of primes of prime index.
A355731 counts choices of a divisor of each prime index, firsts A355732.
A355741 counts choices of a prime factor of each prime index.
Cf. A000079, A007416, A056239, A302540, A319899, A336101, A355739, A370802.

Programs

  • Mathematica
    Select[Range[100],2==PrimeNu[Times @@ PrimePi/@First/@If[#==1,{},FactorInteger[#]]]&]

Formula

A001221(A003963(a(n))) = A303975(a(n)) = 2.
Showing 1-6 of 6 results.

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