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%I #28 Oct 01 2023 07:35:32
%S 2,5,10,13,14,15,31,51,61,67,73
%N Numbers k such that the concatenation of numbers from 1 to k is the product of 3 primes (not necessarily distinct).
%H Patrick De Geest, <a href="http://www.worldofnumbers.com/factorlist.htm">Normal Smarandache Concatenated Numbers, Prime factors from 1 up to n</a>
%H M. Fleuren, <a href="http://www.gallup.unm.edu/~smarandache/michafleuren.htm">Factors and primes of Smarandache sequences</a>.
%H Carlos Rivera, <a href="http://www.primepuzzles.net/puzzles/puzz_008.htm">Puzzle 8. Primes by Listing</a>, The Prime Puzzles & Problems Connection.
%F A046460(a(n)) = 3.
%p q:= n-> is(numtheory[bigomega](parse(cat($1..n)))=3):
%p select(q, [$1..35])[]; # _Alois P. Heinz_, Apr 10 2021
%t Select[Range[100],
%t PrimeOmega@FromDigits@Flatten@IntegerDigits@Range@# == 3 &] (* _Robert Price_, Oct 11 2019 *)
%Y Cf. A001222, A046460.
%K nonn,hard,base
%O 1,1
%A _Patrick De Geest_, Aug 15 1998
%E a(10)-a(11) from _Sean A. Irvine_, Apr 10 2021