login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A020453 Primes that contain digits 1 and 5 only. 6
5, 11, 151, 1151, 1511, 11551, 15511, 15551, 51151, 51511, 51551, 55511, 115151, 511111, 511151, 515111, 1111151, 1115551, 1155151, 1551551, 1555111, 5115511, 5151151, 5151551, 5155511, 5511151, 5511511, 5515151, 5551111, 15511151 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The first 8 terms are also primes when read backward, i.e. in A007500. See also A199325. - M. F. Hasler, Nov 05 2011

LINKS

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

MATHEMATICA

Flatten[Table[Select[FromDigits/@Tuples[{1, 5}, n], PrimeQ], {n, 7}]] (* Vincenzo Librandi, Jul 27 2012 *)

PROG

(PARI) {L=[1, 5]; for(d=1, 9, u=vector(d, i, 10^(d-i))~; forvec(v=vector(d, i, [1, #L]), ispseudoprime(t=vector(d, i, L[v[i]])*u)&print1(t", ")))}  \\ - M. F. Hasler, Nov 05 2011

CROSSREFS

Sequence in context: A266527 A267078 A276511 * A036932 A162252 A179388

Adjacent sequences:  A020450 A020451 A020452 * A020454 A020455 A020456

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 May 6 00:41 EDT 2021. Contains 343579 sequences. (Running on oeis4.)