OFFSET
1,2
COMMENTS
FORMULA
a(n) = A306719(n) - 1.
EXAMPLE
The sequence of terms together with their prime indices begins:
1: {}
3: {2}
7: {4}
9: {2,2}
19: {8}
21: {2,4}
27: {2,2,2}
29: {10}
49: {4,4}
57: {2,8}
63: {2,2,4}
71: {20}
79: {22}
81: {2,2,2,2}
87: {2,10}
107: {28}
113: {30}
133: {4,8}
147: {2,4,4}
171: {2,2,8}
189: {2,2,2,4}
MATHEMATICA
aQ[n_]:=Switch[n, 0, False, 1, True, _, And@@Cases[FactorInteger[n], {p_, k_}:>aQ[PrimePi[p]-1]]];
Select[Range[100], aQ]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Mar 10 2019
STATUS
approved