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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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS 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] CROSSREFS Cf. A068645, A068646, A068647, A068648. Sequence in context: A036936 A002195 A171553 * A158509 A072290 A213691 Adjacent sequences:  A068646 A068647 A068648 * A068650 A068651 A068652 KEYWORD base,nonn AUTHOR Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Feb 28 2002 EXTENSIONS More terms from Sascha Kurz and Harvey P. Dale, Mar 19 2002. The next term has 199 9s sandwiched between the starting and ending 1. STATUS approved

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