OFFSET
1,4
COMMENTS
The Heinz number of a partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k). This gives a bijective correspondence between positive integers and integer partitions.
Starting with n, this is one plus the number of times one must apply A353832 to reach a squarefree number.
EXAMPLE
The trajectory for a(1080) = 4 is the following, with prime indices shown on the right:
1080: {1,1,1,2,2,2,3}
325: {3,3,6}
169: {6,6}
37: {12}
The trajectory for a(87780) = 5 is the following, with prime indices shown on the right:
87780: {1,1,2,3,4,5,8}
65835: {2,2,3,4,5,8}
51205: {3,4,4,5,8}
19855: {3,5,8,8}
2915: {3,5,16}
The trajectory for a(39960) = 5 is the following, with prime indices shown on the right:
39960: {1,1,1,2,2,2,3,12}
12025: {3,3,6,12}
6253: {6,6,12}
1369: {12,12}
89: {24}
MATHEMATICA
Table[If[n==1, 0, Length[NestWhileList[Times@@Prime/@Cases[If[#==1, {}, FactorInteger[#]], {p_, k_}:>PrimePi[p]*k]&, n, !SquareFreeQ[#]&]]], {n, 100}]
CROSSREFS
Positions of 1's are A005117.
Positions of first appearances are A353743.
These are the row-lengths of A353840.
Counting partitions by this statistic gives A353846.
A005811 counts runs in binary expansion.
A318928 gives runs-resistance of binary expansion.
A353832 represents the operation of taking run-sums of a partition.
KEYWORD
nonn
AUTHOR
Gus Wiseman, May 25 2022
STATUS
approved