A337645 a(1)=2; thereafter, a(n) = smallest number with at least two different prime factors that is missing from A336957 after A336957(n) has been found.

2, 6, 10, 10, 10, 10, 10, 10, 10, 18, 20, 20, 20, 20, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 36, 36, 36, 36, 44, 44, 44, 44, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 54

Offset: 1

Author

Scott R. Shannon and N. J. A. Sloane, Sep 25 2020; corrected Oct 11 2020

Keywords

• nonn

Comments

The initial 2 is an exception. For n>2, A336957(n) is required to have at least two different prime factors.

It is conjectured that every number with at least two different prime factors will eventually appear in A336957.

Examples

			A336957 begins 1, 2, 6, 15, 35, 14, with A336957(6)=14. At that point 10 is the smallest legal candidate that has not yet appeared, so a(6) = 10.
		

Links

• N. J. A. Sloane, Table of n, a(n) for n = 1..20000

Crossrefs

Cf. A336957, A338052, A338058.