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Primes that contain digits 1 and 2 only.
10

%I #31 Sep 08 2022 08:44:45

%S 2,11,211,2111,2221,12211,21121,21211,21221,22111,111121,111211,

%T 112111,112121,1111211,1121221,1212121,1212221,1221221,2121121,

%U 2211211,2221111,11221211,12111221,12121121,12121211,12122111,12122221,12212111,12222121

%N Primes that contain digits 1 and 2 only.

%H Vincenzo Librandi, <a href="/A020450/b020450.txt">Table of n, a(n) for n = 1..1000</a>

%t Flatten[Table[Select[FromDigits/@Tuples[{1,2},n],PrimeQ],{n,8}]] (* _Vincenzo Librandi_, Jul 28 2012 *)

%o (PARI) for(nd=1,9, forvec(v=vector(nd,i,[49,50-(i==nd && i>1)]), isprime(t=eval(Strchr(Vecsmall(v)))) && print1(t","))) \\ _M. F. Hasler_, Mar 18 2010

%o (Magma) [p: p in PrimesUpTo(12222121) | Set(Intseq(p)) subset [1, 2]]; // _Vincenzo Librandi_, Jul 28 2012

%o (Python)

%o from sympy import primerange

%o def checkd(a, c):

%o b = set(int(i) for i in set(str(a)))

%o return b.issubset(c)

%o for n in primerange(2, 2000000):

%o if checkd(n, [1, 2]):

%o print(n)

%o # _Abhiram R Devesh_, May 08 2015

%Y Cf. A020449 (digits 0 & 1), ..., A020472 (digits 8 & 9). [From _M. F. Hasler_, Mar 18 2010]

%Y Subsequence of A007931.

%K nonn,base

%O 1,1

%A _David W. Wilson_