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A068685
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Primes which are a sandwich of numbers using at most one digit between two 1's.
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4
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11, 101, 131, 151, 181, 191, 13331, 15551, 16661, 19991, 1333331, 1444441, 1777771, 188888881, 199999991, 1666666666661, 188888888888881, 16666666666666661, 1111111111111111111, 1666666666666666661, 155555555555555555551, 11111111111111111111111
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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11 is a member sandwiching nothing between two 1's. 13331 is a sandwich using 333.
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MATHEMATICA
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Select[Union[Flatten[Table[FromDigits[Join[{1}, PadRight[{}, n, i], {1}]], {n, 0, 20}, {i, 0, 9}]]], PrimeQ] (* Harvey P. Dale, Mar 29 2012 *)
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PROG
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(Python)
from sympy import isprime
from itertools import count, islice
def agen(): yield 11; yield from (t for i in count(1) for m in "0123456789" if isprime(t:=int("1" + m*i + "1")))
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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