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A091189
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Primes of the form 20*R_k + 1, where R_k is the repunit (A002275) of length k.
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2
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OFFSET
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1,1
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COMMENTS
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Primes of the form 222...221.
The number of 2's in each term is given by the corresponding term of A056660 and so the first term too large to include above is 222...2221 (with 120 2's).
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LINKS
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CROSSREFS
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KEYWORD
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bref,nonn
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AUTHOR
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STATUS
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approved
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