A382878 Set of positions of first appearances in A382857 (permutations of prime indices with equal run-lengths).

1, 6, 24, 30, 36, 180, 210, 360, 420, 720, 1080, 1260, 1800, 2160, 2310, 2520, 3600, 4620, 5040, 5400, 6300, 7560, 10800, 12600, 13860, 15120, 21600, 25200, 25920, 27000, 27720, 30030, 32400, 37800, 44100, 45360, 46656, 50400, 54000, 55440, 60060, 60480, 64800

Offset

1,2

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, sum A056239.

Links

Table of n, a(n) for n=1..43.

Example

The permutations for n = 6, 720, 36, 25920, 30:
  (1,2)  (1,2,1,2,1,3,1)  (1,1,2,2)  (1,2,1,2,1,2,1,2,1,3,1)  (1,2,3)
  (2,1)  (1,2,1,3,1,2,1)  (1,2,1,2)  (1,2,1,2,1,2,1,3,1,2,1)  (1,3,2)
         (1,3,1,2,1,2,1)  (2,1,2,1)  (1,2,1,2,1,3,1,2,1,2,1)  (2,1,3)
                          (2,2,1,1)  (1,2,1,3,1,2,1,2,1,2,1)  (2,3,1)
                                     (1,3,1,2,1,2,1,2,1,2,1)  (3,1,2)
                                                              (3,2,1)
The terms together with their prime indices begin:
      1: {}
      6: {1,2}
     24: {1,1,1,2}
     30: {1,2,3}
     36: {1,1,2,2}
    180: {1,1,2,2,3}
    210: {1,2,3,4}
    360: {1,1,1,2,2,3}
    420: {1,1,2,3,4}
    720: {1,1,1,1,2,2,3}
   1080: {1,1,1,2,2,2,3}
   1260: {1,1,2,2,3,4}
   1800: {1,1,1,2,2,3,3}
   2160: {1,1,1,1,2,2,2,3}
   2310: {1,2,3,4,5}
   2520: {1,1,1,2,2,3,4}
   3600: {1,1,1,1,2,2,3,3}

Mathematica

y=Table[Length[Select[Permutations[Join@@ConstantArray@@@FactorInteger[n]], SameQ@@Length/@Split[#]&]], {n, 0, 1000}];
fip[y_]:=Select[Range[Length[y]], !MemberQ[Take[y, #-1], y[[#]]]&];
fip[Rest[y]]

Crossrefs

Positions of first appearances in A382857 (zeros A382879), by signature A382858.

For distinct run-lengths we have A382772, firsts of A382771 (by signature A382773).

A140690 lists numbers whose binary expansion has equal run-lengths, distinct A044813.

A056239 adds up prime indices, row sums of A112798.

A239455 counts Look-and-Say partitions, ranks A351294, conjugate A381432.

A329738 counts compositions with equal run-lengths, ranks A353744.

A329739 counts compositions with distinct run-lengths, ranks A351596.

A351293 counts non-Look-and-Say partitions, ranks A351295, conjugate A381433.

Cf. A000720, A001221, A001222, A003242, A048767, A098859, A130091, A238130, A305936, A351013, A351202, A382876.

Sequence in context: A383413 A249667 A114274 * A335215 A292985 A335197

Adjacent sequences: A382875 A382876 A382877 * A382879 A382880 A382881

Keyword

nonn

Author

Gus Wiseman, Apr 09 2025

Status

approved