A092624 Numbers with exactly two prime digits.

22, 23, 25, 27, 32, 33, 35, 37, 52, 53, 55, 57, 72, 73, 75, 77, 122, 123, 125, 127, 132, 133, 135, 137, 152, 153, 155, 157, 172, 173, 175, 177, 202, 203, 205, 207, 212, 213, 215, 217, 220, 221, 224, 226, 228, 229, 230, 231, 234, 236, 238, 239, 242, 243, 245

Offset

1,1

Comments

A193238(a(n))=2; subsequence of A118950. [Reinhard Zumkeller, Jul 19 2011]

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Example

25 has two prime digits, 2 and 5;
207 has two prime digits, 2 and 7.

Maple

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);

Prog

(Haskell)
import Data.List (elemIndices)
a092624 n = a092624_list !! (n-1)
a092624_list = elemIndices 2 a193238_list
-- Reinhard Zumkeller, Jul 19 2011

Crossrefs

Cf. A034895, A046034, A085557, A019546, A034844.

Cf. A084984, A092620, A092625.

Sequence in context: A034895 A106582 A092619 * A254751 A260993 A276182

Adjacent sequences: A092621 A092622 A092623 * A092625 A092626 A092627

Keyword

nonn,base

Author

Jani Melik, Apr 11 2004

Status

approved