login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A020450 Primes that contain digits 1 and 2 only. 7
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

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

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)

import sympy

def checkd(a, c):

....b=[int(i) for i in list(set(list(str(a))))]

....return(set(b).issubset(c))

n=2

while n>1:

....if checkd(n, [1, 2])==True:

........print(n)

....n=sympy.nextprime(n)

// Abhiram R Devesh, May 08 2015

CROSSREFS

Cf. A020449 (digits 0 & 1), ..., A020472 (digits 8 & 9). [From M. F. Hasler, Mar 18 2010]

Sequence in context: A051663 A188203 A070256 * A036229 A104337 A283512

Adjacent sequences:  A020447 A020448 A020449 * A020451 A020452 A020453

KEYWORD

nonn,base

AUTHOR

David W. Wilson

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 18 22:08 EDT 2019. Contains 322237 sequences. (Running on oeis4.)