OFFSET
1,1
COMMENTS
First differs from A061345 at a(1) = 2 and next at a(98) = 441.
A number n is in the sequence iff n = 2 or the prime indices of n have a common divisor > 1 and the Heinz number of the multiset of prime multiplicities of n, namely A181819(n), is already in the sequence.
The Heinz number of an integer partition (y_1, ..., y_k) is prime(y_1) * ... * prime(y_k).
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..2326
EXAMPLE
The sequence of partitions whose Heinz numbers belong to the sequence begins: (1), (2), (3), (4), (2,2), (5), (6), (7), (8), (9), (3,3), (2,2,2), (10), (11), (12), (13), (14), (15), (4,4), (16), (17), (18), (19), (20), (21), (22), (2,2,2,2).
MATHEMATICA
supperQ[n_]:=Or[n==2, And[GCD@@PrimePi/@FactorInteger[n][[All, 1]]>1, supperQ[Times@@Prime/@FactorInteger[n][[All, 2]]]]];
Select[Range[500], supperQ]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 12 2018
STATUS
approved