A068650 Primes in which a string of 1's is sandwiched between two 3's.
313, 3111111111113, 311111111111113, 3111111111111111111111111111113, 311111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111113
Offset: 1
Links
- Harvey P. Dale, Table of n, a(n) for n = 1..8
- Patrick De Geest, PDP Reference Table - 313.
- Makoto Kamada, Prime numbers of the form 311...113.
- Index entries for primes involving repunits.
Programs
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Maple
a := 3:b := 1: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[10*FromDigits[PadRight[{3},n,1]]+3,{n,2,110}],PrimeQ] (* Harvey P. Dale, Dec 18 2022 *)
Extensions
More terms from Sascha Kurz, Mar 19 2002
Edited by Ray Chandler, Nov 04 2014
Comments