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Positions of 2's in A048288.
4

%I #21 Oct 01 2023 07:25:40

%S 2,3,4,6,7,11

%N Positions of 2's in A048288.

%H Patrick De Geest, <a href="http://www.worldofnumbers.com/revfact.htm">Reversed Smarandache Concatenated Numbers, Prime factors from n down to 1</a>

%H M. Fleuren, <a href="http://www.gallup.unm.edu/~smarandache/michafleuren.htm">Factors and primes of Smarandache sequences</a>.

%H M. Fleuren, <a href="http://www.gallup.unm.edu/~smarandache/micha.txt">Smarandache Factors and Reverse factors</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.

%t Select[Range[2,12],PrimeOmega[FromDigits[Flatten[IntegerDigits[Range[#,1,-1]]]]]==2 &] (* _Jayanta Basu_, May 30 2013 *)

%Y Cf. A000422, A046461, A048288, A050680, A050681, A050682.

%K nonn,base,hard,more

%O 1,1

%A _Patrick De Geest_, Aug 15 1999

%E Offset changed to 1 by _Jinyuan Wang_, Sep 04 2021