A337645 - OEIS

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

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OFFSET

1,1

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.

LINKS

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

EXAMPLE

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.

CROSSREFS

Cf. A336957, A338052, A338058.