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A068649
Primes in which a string of 9's is sandwiched between two 1's.
2
11, 191, 19991, 199999991, 19999999999999999999999999999999999999991, 199999999999999999999999999999999999999999999999999999999999999999999999999999999999991
OFFSET
1,1
COMMENTS
The next term has 199 9's sandwiched between the starting and ending 1.
EXAMPLE
11 is also a member in which a string of 0 9's is there between two one's.
MAPLE
a := 1:b := 9: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[FromDigits[Join[{1}, Table[9, {i}], {1}]], {i, 0, 200}], PrimeQ]
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Feb 28 2002
EXTENSIONS
More terms from Sascha Kurz and Harvey P. Dale, Mar 19 2002
Edited by Ray Chandler, Nov 04 2014
STATUS
approved