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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A240680 Primes p such that p*10+k is prime for exactly three values of the digit k. 4
 7, 13, 31, 43, 61, 103, 109, 199, 271, 367, 409, 421, 523, 541, 547, 787, 823, 829, 883, 1009, 1033, 1117, 1237, 1291, 1669, 1999, 2131, 2161, 2203, 2269, 2437, 2503, 2593, 2671, 2857, 3049, 3253, 3271, 3361, 3559, 3583, 3769, 3823, 4003, 4201, 4339, 4357 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Bruno Berselli, Table of n, a(n) for n = 1..1000 EXAMPLE 7 is in the sequence because 71, 73 and 79 are prime, but 77 is not prime. PROG (PARI) forprime(p=2, 10000, t=0; forstep(k=1, 9, 2, if(isprime(p*10+k), t++)); if(t==3, print1(p, ", "))) (MAGMA) [p: p in PrimesUpTo(10^4) | {k: k in [1, 3, 7, 9] | IsPrime(p*10+k)} in Subsets({1, 3, 7, 9}, 3)]; // Bruno Berselli, Apr 10 2014 CROSSREFS Cf. A067267, A119289, A240678, A240679, A240689. Sequence in context: A231626 A343302 A110912 * A308851 A298027 A085104 Adjacent sequences:  A240677 A240678 A240679 * A240681 A240682 A240683 KEYWORD nonn,base AUTHOR Colin Barker, Apr 10 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 | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 15 06:12 EDT 2021. Contains 342975 sequences. (Running on oeis4.)