The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A090710 Primes with digits less than 7 whose decimal representation is also a prime when interpreted in base 7. 9
 2, 3, 5, 23, 41, 43, 61, 113, 131, 241, 313, 401, 421, 443, 461, 463, 661, 1013, 1033, 1051, 1123, 1231, 1301, 1433, 1453, 1543, 1613, 2111, 2131, 2153, 2203, 2333, 2441, 2531, 2551, 3121, 3163, 3251, 3323, 3433, 3541, 4001, 4111, 4153, 4201, 4241, 4421 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Note that the definition of, e.g., A090714 works "the other way round". - M. F. Hasler, Jan 03 2014 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 EXAMPLE 23 is a prime and a valid number in base 7, and 23 [base 7] = 17 [base 10] is again a prime. MATHEMATICA Select[ FromDigits@# & /@ IntegerDigits[ Prime@ Range@ 270, 7], PrimeQ] (* Robert G. Wilson v, Jan 05 2014 *) FromDigits/@Select[Tuples[{0, 1, 2, 3, 4, 5, 6}, 4], AllTrue[ {FromDigits[ #], FromDigits[ #, 7]}, PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Dec 29 2015 *) PROG (PARI) is_A090710(p, b=7)=vecmax(d=digits(p))t, for(j=i, #d, d[j]=t); break)); fromdigits(d, newBase) list(lim)=my(v=List(), t); forprime(p=2, fixBase(lim\1, 10, 7), if(isprime(t=fromdigits(digits(p, 7), 10)), listput(v, t))); Vec(v) \\ Charles R Greathouse IV, Nov 07 2016 CROSSREFS Cf. A031974, A089971, A089981, A090707, A090708, A090709, A235394, A235395, A000040. Sequence in context: A215313 A215317 A104736 * A153477 A080016 A171432 Adjacent sequences: A090707 A090708 A090709 * A090711 A090712 A090713 KEYWORD base,nonn AUTHOR Cino Hilliard, Jan 18 2004 EXTENSIONS Name, example and offset corrected by M. F. Hasler, Jan 03 2014 STATUS approved

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

Last modified December 1 07:20 EST 2022. Contains 358454 sequences. (Running on oeis4.)