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A068649
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Primes in which a string of 9's is sandwiched between two 1's.
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2
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11, 191, 19991, 199999991, 19999999999999999999999999999999999999991, 199999999999999999999999999999999999999999999999999999999999999999999999999999999999991
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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EXAMPLE
| 11 is also a member in which a string of 0 9's is there between two one's.
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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);
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MATHEMATICA
| Select[Table[FromDigits[Join[{1}, Table[9, {i}], {1}]], {i, 0, 200}], PrimeQ]
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CROSSREFS
| Cf. A068645, A068646, A068647, A068648.
Sequence in context: A036936 A002195 A171553 * A158509 A072290 A112127
Adjacent sequences: A068646 A068647 A068648 * A068650 A068651 A068652
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KEYWORD
| base,nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Feb 28 2002
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EXTENSIONS
| More terms from Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de) and Harvey P. Dale (hpd1(AT)nyu.edu), Mar 19 2002.
The next term has 199 9s sandwiched between the starting and ending 1.
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