A068646 Primes in which a string of 5's is sandwiched between two 1's.
11, 151, 15551, 155555555555555555551, 155555555555555555555555555555551
Offset: 1
Examples
11 is also a member in which a string of 0 5's is there between two one's.
Links
- Patrick De Geest, PDP Reference Table - 151.
- Makoto Kamada, Prime numbers of the form 155...551.
- Index entries for primes involving repunits.
Programs
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Maple
a := 1:b := 5:i := 1:for n from 0 to 500 do c := a+10*(10^n-1)/9*b+10^(n+1)*a; if(isprime(c)) then d[i] := c; i := i+1; end if; end do:q := seq(d[j],j=1..i-1);
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Mathematica
Select[Table[FromDigits[Join[PadRight[{1},n,5],{1}]],{n,500}],PrimeQ] (* Harvey P. Dale, Aug 08 2012 *)
Extensions
More terms from Sascha Kurz, Mar 19 2002
Edited by Ray Chandler, Nov 04 2014
Comments