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.
EXAMPLE
The terms together with their prime indices begin:
1: {}
2: {1}
3: {2}
7: {4}
13: {6}
37: {12}
53: {16}
89: {24}
151: {36}
223: {48}
281: {60}
311: {64}
659: {120}
827: {144}
1069: {180}
1163: {192}
1511: {240}
2045: {3,80}
2423: {360}
3241: {4,90}
4211: {576}
5443: {720}
6473: {840}
6997: {900}
7561: {960}
9037: {4,210}
MATHEMATICA
rnnm[q_]:=Max@@Select[Range[Min@@q, Max@@q], SubsetQ[q, Range[#]]&];
posfirsts[q_]:=Table[Position[q, n][[1, 1]], {n, Min@@q, rnnm[q]}];
posfirsts[Table[Length[Union @@ Divisors/@PrimePi/@First/@If[n==1, {}, FactorInteger[n]]], {n, 1000}]]//Sort
CROSSREFS
The unsorted version is A371131.
A000005 counts divisors.
A001221 counts distinct prime factors.
A003963 gives product of prime indices.
A355741 counts choices of a prime factor of each prime index.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Mar 20 2024
STATUS
approved