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 A217064 Primes that remain prime when a single "5" digit is inserted between any two adjacent decimal digits. 2
 11, 17, 47, 71, 83, 89, 149, 167, 179, 251, 257, 293, 347, 359, 383, 419, 461, 467, 491, 557, 563, 569, 653, 773, 911, 1193, 1217, 1277, 1451, 1559, 1667, 1823, 1901, 2243, 2309, 2357, 2579, 2657, 2999, 3527, 3533, 4289, 5051, 5351, 5501, 5843, 6089, 6551, 6581 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Paolo P. Lava, Table of n, a(n) for n = 1..140 EXAMPLE 290183  is prime and also 2901853, 2901583, 2905183, 2950183 and 2590183. MAPLE with(numtheory); A217064:=proc(q, x) local a, b, c, i, n, ok; for n from 5 to q do   a:=ithprime(n); b:=0; while a>0 do b:=b+1; a:=trunc(a/10); od; a:=ithprime(n); ok:=1;     for i from 1 to b-1 do       c:=a+9*10^i*trunc(a/10^i)+10^i*x;  if not isprime(c) then ok:=0; break; fi; od;     if ok=1 then print(ithprime(n)); fi; od; end: A217064(1000000, 5); PROG (PARI) is(n)=my(v=concat([""], digits(n))); for(i=2, #v-1, v[1]=Str(v[1], v[i]); v[i]=5; if(i>2, v[i-1]=""); if(!isprime(eval(concat(v))), return(0))); isprime(n) \\ Charles R Greathouse IV, Sep 26 2012 CROSSREFS Cf. A050674, A050711-A050719, A069246, A159236, A215417, A215419-A215421, A217044-A217047, A217062, A217063, A217065 Sequence in context: A248482 A267772 A046122 * A242244 A228031 A324795 Adjacent sequences:  A217061 A217062 A217063 * A217065 A217066 A217067 KEYWORD nonn,base AUTHOR Paolo P. Lava, Sep 26 2012 STATUS approved

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Last modified January 26 17:31 EST 2020. Contains 331280 sequences. (Running on oeis4.)