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A092622 Primes with exactly two prime digits. 0
23, 37, 53, 73, 127, 137, 157, 173, 229, 239, 251, 263, 271, 283, 293, 307, 313, 317, 331, 347, 359, 367, 379, 383, 397, 433, 457, 503, 521, 547, 563, 571, 587, 593, 653, 673, 677, 739, 743, 751, 787, 797, 823, 827, 853, 857, 877, 937, 953, 977, 1033, 1123 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..52.

FORMULA

a(n) >> n^1.285

EXAMPLE

23 is prime and it has two prime digits, 2 and 3;

127 is prime and it 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_prnd:=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) = 2) then ans:=[ op(ans), i ]: tren:=tren+1; fi od; RETURN(ans) end: ts_pr_prnd(2500);

CROSSREFS

Cf. A034844.

Sequence in context: A066064 A163759 A190731 * A129351 A179910 A124888

Adjacent sequences:  A092619 A092620 A092621 * A092623 A092624 A092625

KEYWORD

nonn,base

AUTHOR

Jani Melik, Apr 11 2004

STATUS

approved

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Last modified February 19 20:54 EST 2019. Contains 320328 sequences. (Running on oeis4.)