A046465 Numbers k such that the concatenation of numbers from 1 to k is the product of 6 primes (not necessarily distinct).

11, 12, 18, 19, 22, 24, 32, 33, 39, 49, 57, 65, 70, 71, 75, 76, 78, 79, 81, 83, 85, 87, 88, 91, 95, 96, 99, 105, 110

Offset: 1

Author

Patrick De Geest, Aug 15 1998

Keywords

• nonn
• base
• hard
• more

Links

• Patrick De Geest, Normal Smarandache Concatenated Numbers, Prime factors from 1 up to n
• M. Fleuren, Smarandache Factors and Reverse factors
• Carlos Rivera, Puzzle 8. Primes by Listing, The Prime Puzzles & Problems Connection.

Crossrefs

Cf. A046460.

Programs

Mathematica

Select[Range[100], PrimeOmega@FromDigits@Flatten@IntegerDigits@Range@# == 6 &] (* Robert Price, Oct 11 2019 *)

Extensions

a(12)-a(29) from Sean A. Irvine, Apr 10 2021