A046466 Numbers k such that the concatenation of numbers from 1 to k is the product of 7 primes (not necessarily distinct).
28, 30, 42, 44, 46, 69, 72, 82, 84, 86, 93, 109, 116
Offset: 1
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
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Mathematica
Select[Range[100], PrimeOmega@FromDigits@Flatten@IntegerDigits@Range@# == 7 &] (* Robert Price, Oct 11 2019 *)
Extensions
a(6)-a(13) from Sean A. Irvine, Apr 10 2021