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A247098 Smallest prime p that generates n different primes if p is prepended to, inserted into, or appended to p. 0
2, 109, 131, 10289, 12197, 1227797, 101636629, 118561139 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(8)>10^9.

LINKS

Table of n, a(n) for n=0..7.

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

with(numtheory): P:=proc(q, x) local b, c, f, g, h, j, k, n, t, v; t:=0;

v:=array(1..x); for k from 1 to x do v[k]:=0; od; print(2);

for n from 3 by 2 to q do if isprime(n) then b:=ilog10(n)+1; h:=0;

for j from 0 to ilog10(n)+1 do f:=(n mod 10^j);

if j=0 then c:=n*10^b+n; else g:=n*10^j+f;

c:=trunc(n/10^j)*10^(j+b)+g; if isprime(c) then h:=h+1; fi; fi; od;

if h>t then if h=t+1 then t:=t+1; print(n);

while v[t+1]>0 do t:=t+1; print(v[t]); od;

else if v[h]=0 then v[h]:=n; fi; fi; fi; fi; od; end: P(10^9, 30);

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

STATUS

approved

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Last modified October 16 12:00 EDT 2018. Contains 316263 sequences. (Running on oeis4.)