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A020450 Primes that contain digits 1 and 2 only. 10
2, 11, 211, 2111, 2221, 12211, 21121, 21211, 21221, 22111, 111121, 111211, 112111, 112121, 1111211, 1121221, 1212121, 1212221, 1221221, 2121121, 2211211, 2221111, 11221211, 12111221, 12121121, 12121211, 12122111, 12122221, 12212111, 12222121 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
MATHEMATICA
Flatten[Table[Select[FromDigits/@Tuples[{1, 2}, n], PrimeQ], {n, 8}]] (* Vincenzo Librandi, Jul 28 2012 *)
PROG
(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
(Magma) [p: p in PrimesUpTo(12222121) | Set(Intseq(p)) subset [1, 2]]; // Vincenzo Librandi, Jul 28 2012
(Python)
from sympy import primerange
def checkd(a, c):
b = set(int(i) for i in set(str(a)))
return b.issubset(c)
for n in primerange(2, 2000000):
if checkd(n, [1, 2]):
print(n)
# Abhiram R Devesh, May 08 2015
CROSSREFS
Cf. A020449 (digits 0 & 1), ..., A020472 (digits 8 & 9). [From M. F. Hasler, Mar 18 2010]
Subsequence of A007931.
Sequence in context: A188203 A070256 A356523 * A036229 A104337 A283512
KEYWORD
nonn,base
AUTHOR
STATUS
approved

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Last modified July 23 08:23 EDT 2024. Contains 374546 sequences. (Running on oeis4.)