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A068650
Primes in which a string of 1's is sandwiched between two 3's.
5
313, 3111111111113, 311111111111113, 3111111111111111111111111111113, 311111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111113
OFFSET
1,1
COMMENTS
The next term (a(6)) has 127 digits. - Harvey P. Dale, Dec 18 2022
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);
MATHEMATICA
Select[Table[10*FromDigits[PadRight[{3}, n, 1]]+3, {n, 2, 110}], PrimeQ] (* Harvey P. Dale, Dec 18 2022 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Feb 28 2002
EXTENSIONS
More terms from Sascha Kurz, Mar 19 2002
Edited by Ray Chandler, Nov 04 2014
STATUS
approved