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A089785
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a(n) is the least prime(k) such that the concatenation of prime(k) and prime(k-n) is prime.
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3
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5, 7, 11, 19, 17, 19, 23, 29, 31, 37, 67, 43, 83, 61, 59, 61, 67, 79, 73, 113, 97, 167, 107, 101, 103, 149, 109, 137, 167, 163, 137, 179, 149, 163, 257, 179, 277, 173, 251, 199, 191, 193, 197, 199, 211, 229, 227, 229, 233, 239, 281, 347, 283, 263, 269, 271, 283
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(4) = 19 =prime(8) and prime(8) followed by prime(8-4) =197 is prime.
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MAPLE
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f:= proc(n) local p, k, q, d;
p:= ithprime(n);
for k from n+1 do
p:= nextprime(p);
q:= ithprime(k-n);
d:= ilog10(q)+1;
if isprime(p*10^d+q) then return p fi
od
end proc:
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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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