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A092624 Numbers with exactly two prime digits.

%I A092624 #12 Apr 20 2025 10:47:29
%S A092624 22,23,25,27,32,33,35,37,52,53,55,57,72,73,75,77,122,123,125,127,132,
%T A092624 133,135,137,152,153,155,157,172,173,175,177,202,203,205,207,212,213,
%U A092624 215,217,220,221,224,226,228,229,230,231,234,236,238,239,242,243,245
%N A092624 Numbers with exactly two prime digits.
%C A092624 A193238(a(n))=2; subsequence of A118950. [_Reinhard Zumkeller_, Jul 19 2011]
%H A092624 Reinhard Zumkeller, <a href="/A092624/b092624.txt">Table of n, a(n) for n = 1..10000</a>
%e A092624 25 has two prime digits, 2 and 5;
%e A092624 207 has two prime digits, 2 and 7.
%p A092624 stev_sez:=proc(n) local i, tren, st, ans, anstren; ans:=[ ]: anstren:=[ ]: tren:=n: for i while (tren>0) do st:=round( 10*frac(tren/10) ): ans:=[ op(ans), st ]: tren:=trunc(tren/10): end do; for i from nops(ans) to 1 by -1 do anstren:=[ op(anstren), op(i,ans) ]; od; RETURN(anstren); end: ts_stpf:=proc(n) local i, stpf, ans; ans:=stev_sez(n): stpf:=0: for i from 1 to nops(ans) do if (isprime(op(i,ans))='true') then stpf:=stpf+1; # number of prime digits fi od; RETURN(stpf) end: ts_pr_nd:=proc(n) local i, stpf, ans, ans1, tren; ans:=[ ]: stpf:=0: tren:=1: for i from 1 to n do if ( ts_stpf(i) = 2) then ans:=[ op(ans), i ]: tren:=tren+1; fi od; RETURN(ans) end: ts_pr_nd(500);
%t A092624 Select[Range[300],Count[IntegerDigits[#],_?PrimeQ]==2&] (* _Harvey P. Dale_, Apr 20 2025 *)
%o A092624 (Haskell)
%o A092624 import Data.List (elemIndices)
%o A092624 a092624 n = a092624_list !! (n-1)
%o A092624 a092624_list = elemIndices 2 a193238_list
%o A092624 -- _Reinhard Zumkeller_, Jul 19 2011
%Y A092624 Cf. A034895, A046034, A085557, A019546, A034844.
%Y A092624 Cf. A084984, A092620, A092625.
%K A092624 nonn,base
%O A092624 1,1
%A A092624 _Jani Melik_, Apr 11 2004