A046464 Numbers k such that the concatenation of numbers from 1 to k is the product of 5 primes (not necessarily distinct).
8, 17, 25, 41, 47, 55, 56, 63, 77, 94, 101, 103, 107
Offset: 1
Links
- Patrick De Geest, Normal Smarandache Concatenated Numbers, Prime factors from 1 up to n
- M. Fleuren, Factors and primes of Smarandache sequences.
- M. Fleuren, Smarandache Factors and Reverse factors
- Carlos Rivera, Puzzle 8. Primes by Listing, The Prime Puzzles & Problems Connection.
Programs
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Mathematica
Select[Range[100],PrimeOmega@FromDigits@Flatten@ IntegerDigits@ Range@# == 5 &] (* Robert Price, Oct 11 2019 *)
Extensions
a(9)-a(13) from Sean A. Irvine, Apr 10 2021