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

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A069090 Primes none of whose proper initial segments are primes. 6
 2, 3, 5, 7, 11, 13, 17, 19, 41, 43, 47, 61, 67, 83, 89, 97, 101, 103, 107, 109, 127, 149, 151, 157, 163, 167, 181, 401, 409, 421, 443, 449, 457, 461, 463, 467, 487, 491, 499, 601, 607, 631, 641, 643, 647, 653, 659, 661, 683, 691, 809, 811, 821, 823, 827, 829 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Franklin T. Adams-Watters and R. Zumkeller, Table of n, a(n) for n = 1..10000 (first 1000 terms from Franklin T. Adams-Watters) Barry Carter, Table of n, a(n) for n = 1..1411151 (bz2 compressed) Barry Carter, Mathematica program StackExchange, Number of digits until a prime is reached EXAMPLE The proper initial segments of 499 are 4 and 49, none of which are primes. So 499 is a term of the sequence. MAPLE isA069090 := proc(n)     local dgs, l ;     if isprime(n) then         dgs := convert(n, base, 10) ;         ndgs := nops(dgs) ;         for l from 1 to ndgs-1 do             add( op(ndgs+i-l+1, dgs)*10^i, i=0..l-1) ;             if isprime(%) then                 return false;             end if;         end do:         true ;     else         false ;     end if; end proc: for n from 2 to 830 do     if isA069090(n) then         printf("%d, ", n);     end if; end do: # R. J. Mathar, Dec 15 2016 MATHEMATICA Select[Prime[Range[200]], NoneTrue[FromDigits/@Table[Take[ IntegerDigits[ #], n], {n, IntegerLength[#]-1}], PrimeQ]&] (* The program uses the NoneTrue function from Mathematica version 10 *) (* Harvey P. Dale, Jul 24 2016 *) PROG (PARI) ina(n)=if(!isprime(n), return(0)); while(n>9, n\=10; if(isprime(n), return(0))); 1 \\ Franklin T. Adams-Watters, Jun 26 2009 (Haskell) import Data.List (inits) a069090 n = a069090_list !! (n-1) a069090_list = filter    (all (== 0) . map (a010051 . read) . init . tail . inits . show)    a000040_list -- Reinhard Zumkeller, Mar 11 2014 CROSSREFS Cf. A074721. [Franklin T. Adams-Watters, Jun 26 2009] Cf. A000040, A010051. Sequence in context: A216496 A069709 A144755 * A321150 A088415 A175063 Adjacent sequences:  A069087 A069088 A069089 * A069091 A069092 A069093 KEYWORD base,nonn AUTHOR Joseph L. Pe, Apr 05 2002 EXTENSIONS More terms from Franklin T. Adams-Watters, Jun 26 2009 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.

Last modified January 23 04:16 EST 2020. Contains 331168 sequences. (Running on oeis4.)