A335433 Numbers whose multiset of prime indices is separable.

1, 2, 3, 5, 6, 7, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 26, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 50, 51, 52, 53, 55, 57, 58, 59, 60, 61, 62, 63, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 82, 83

Offset

1,2

Comments

First differs from A212167 in having 72.

Includes all squarefree numbers A005117.

A multiset is separable if it has a permutation that is an anti-run, meaning there are no adjacent equal parts.

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 separable partitions (A325534). The Heinz number of an integer partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k).

Also numbers that cannot be written as a product of prime numbers, each different from the last but not necessarily different from those prior to the last.

Links

Table of n, a(n) for n=1..67.

Example

The sequence of terms together with their prime indices begins:
      1: {}          20: {1,1,3}       39: {2,6}
      2: {1}         21: {2,4}         41: {13}
      3: {2}         22: {1,5}         42: {1,2,4}
      5: {3}         23: {9}           43: {14}
      6: {1,2}       26: {1,6}         44: {1,1,5}
      7: {4}         28: {1,1,4}       45: {2,2,3}
     10: {1,3}       29: {10}          46: {1,9}
     11: {5}         30: {1,2,3}       47: {15}
     12: {1,1,2}     31: {11}          50: {1,3,3}
     13: {6}         33: {2,5}         51: {2,7}
     14: {1,4}       34: {1,7}         52: {1,1,6}
     15: {2,3}       35: {3,4}         53: {16}
     17: {7}         36: {1,1,2,2}     55: {3,5}
     18: {1,2,2}     37: {12}          57: {2,8}
     19: {8}         38: {1,8}         58: {1,10}

Mathematica

primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[100], Select[Permutations[primeMS[#]], !MatchQ[#, {___, x_, x_, ___}]&]!={}&]

Crossrefs

The version for a multiset with prescribed multiplicities is A335127.

Separable factorizations are counted by A335434.

The complement is A335448.

Separations are counted by A003242 and A335452 and ranked by A333489.

Permutations of prime indices are counted by A008480.

Inseparable partitions are counted by A325535.

Strict permutations of prime indices are counted by A335489.

Cf. A000961, A005117, A056239, A112798, A114938, A181796, A292884, A335407, A335451, A335516.

Sequence in context: A052485 A341646 A109421 * A345172 A212167 A339741

Adjacent sequences: A335430 A335431 A335432 * A335434 A335435 A335436

Keyword

nonn

Author

Gus Wiseman, Jul 02 2020

Status

approved