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A090920
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Primes of the form n followed by the least k == 1 (mod n).
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1
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11, 23, 31, 41, 521, 61, 71, 89, 919, 101, 1123, 1213, 131, 1429, 151, 1697, 17137, 181, 191, 2081, 211, 2267, 2347, 241, 251, 26183, 271, 281, 29581, 3061, 311, 32257, 331, 3469, 3571, 3637, 37223, 3877, 39157, 401, 41411, 421, 431, 44221, 4591, 461, 47189
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OFFSET
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1,1
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COMMENTS
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Conjecture: For n > 1, if a(n) = n concatenated with k then k < n^2.
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LINKS
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Robert Israel, Table of n, a(n) for n = 1..10000
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EXAMPLE
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a(5) = 521, as 51,56,511 and 516 are all composite.
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MAPLE
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f:= proc(n) local k, p;
for k from 1 by n do
p:= n*10^(1+ilog10(k))+k;
if isprime(p) then return p fi
od
end proc:
map(f, [$1..100]); # Robert Israel, Jan 13 2017
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PROG
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(PARI) a(n)=my(t); forstep(k=1, oo, n, if(isprime(t=10^#digits(k)*n+k), return(t))) \\ Charles R Greathouse IV, Jan 13 2017
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CROSSREFS
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Cf. A068695.
Sequence in context: A030675 A110786 A059642 * A344175 A126330 A090506
Adjacent sequences: A090917 A090918 A090919 * A090921 A090922 A090923
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KEYWORD
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base,nonn
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AUTHOR
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Amarnath Murthy, Dec 16 2003
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EXTENSIONS
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More terms from David Wasserman, Feb 14 2006
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STATUS
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approved
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