A092623 Primes with exactly three prime digits.
223, 227, 233, 257, 277, 337, 353, 373, 523, 557, 577, 727, 733, 757, 773, 1223, 1237, 1277, 1327, 1373, 1523, 1553, 1723, 1733, 1753, 1777, 2027, 2053, 2137, 2153, 2203, 2207, 2213, 2221, 2239, 2243, 2251, 2267, 2287, 2293, 2297, 2339, 2347, 2351, 2371
Offset: 1
Examples
223 is prime and it has three prime digits 2,2,3; 1237 is prime and it has three prime digits 2,3,7;
Programs
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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_prnt:=proc(n) local i, stpf, ans, ans1, tren; ans:=[ ]: stpf:=0: tren:=1: for i from 1 to n do if ( isprime(i)='true' and ts_stpf(i) = 3) then ans:=[ op(ans), i ]: tren:=tren+1; fi od; RETURN(ans) end: ts_pr_prnt(5000);
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Mathematica
Select[Prime[Range[400]],Count[IntegerDigits[#],?PrimeQ]==3&] (* _Harvey P. Dale, Dec 27 2011 *)
Formula
a(n) >> x^1.285