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!)
 A247098 Smallest prime p that generates n different primes if it is inserted into p itself. 1
 2, 109, 131, 10289, 12197, 1227797, 101636629, 118561139, 10596073217, 89466662147, 37898818253 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(8) > 10^9. The concatenation of p with p will not result in a prime as the result is divisible by 10^k+1, where k is the number of digits in p. - Chai Wah Wu, Jun 25 2019 LINKS EXAMPLE a(0) = 2 is prime but concat(2,2) = 22 is not. a(1) = 109 is prime and also concat(1,109,09) = 110909. a(2) = 131 is prime. Again, concat(13,131,1) = 131311 is prime and also concat(1,131,31) = 113131. a(5) = 1227797 and the five primes that are generated are: 12277912277977, 12271227797797, 12212277977797, 12122779727797, 11227797227797. MAPLE P:=proc(q) local a, b, i, j, k, n, t: print(2); for j from 1 to q do n:=2: for k from 1 to q do n:=nextprime(n): b:=length(n): t:=0: for i from 1 to b-1 do if isprime((trunc(n/10^i)*10^b+n)*10^i+(n mod 10^i)) then t:=t+1; fi; od;  if t=j then print(n); break; fi; od; od; end: P(10^9); CROSSREFS Cf. A250311, A250312. Sequence in context: A111456 A157067 A287153 * A245056 A023281 A042457 Adjacent sequences:  A247095 A247096 A247097 * A247099 A247100 A247101 KEYWORD nonn,base,more AUTHOR Paolo P. Lava, Nov 18 2014 EXTENSIONS a(8)-a(10) from Chai Wah Wu, Jul 01 2019 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 12 10:52 EDT 2021. Contains 342920 sequences. (Running on oeis4.)