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 A089785 a(n) is the least prime(k) such that the concatenation of prime(k) and prime(k-n) is prime. 3
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE a(4) = 19 =prime(8) and prime(8) followed by prime(8-4) =197 is prime. MAPLE 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: map(f, [\$1..100]); # Robert Israel, Dec 13 2017 CROSSREFS Cf. A089782, A089783. Sequence in context: A027755 A260828 A280651 * A226383 A118386 A240849 Adjacent sequences:  A089782 A089783 A089784 * A089786 A089787 A089788 KEYWORD base,nonn AUTHOR Amarnath Murthy, Nov 24 2003 EXTENSIONS More terms from David Wasserman, Oct 13 2005 STATUS approved

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Last modified April 23 12:15 EDT 2021. Contains 343204 sequences. (Running on oeis4.)