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 A340539 a(n) is the least prime that is the concatenation of two n-digit primes, and such that the concatenation of the same primes in the other order is also prime or 0 if no such prime exists. 1
 37, 1123, 101107, 10091789, 1000710709, 100003100363, 10000031000303, 1000001910002521, 100000007100010321, 10000000071000000349, 1000000001910000000799, 100000000003100000009939, 10000000000391000000012387, 1000000000003710000000034573, 100000000000031100000000014113 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Conjecture: a(n) > 0 and for n > 1 the first n digits of a(n) = A003617(n). - Chai Wah Wu, Jan 13 2021 LINKS Robert Israel, Table of n, a(n) for n = 1..171 EXAMPLE For n=4, 1009, 1789, 10091789 and 17891009 are all prime. MAPLE f:= proc(d) local P, a, b;   a:= prevprime(10^(d-1));   do     a:= nextprime(a);     if a > 10^d then return FAIL fi;     b:= prevprime(10^(d-1));     do       b:= nextprime(b);       if b > 10^d then break fi;       if isprime(10^d*a+b) and isprime(10^d*b+a) then return 10^d*a+b fi;   od od:   FAIL end proc: f(1):= 37: map(f, [\$1..20]); CROSSREFS Cf. A003617, A340487. Sequence in context: A253245 A168166 A168165 * A219309 A099201 A218841 Adjacent sequences:  A340536 A340537 A340538 * A340540 A340541 A340542 KEYWORD nonn,base AUTHOR J. M. Bergot and Robert Israel, Jan 10 2021 STATUS approved

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Last modified January 28 04:30 EST 2022. Contains 350654 sequences. (Running on oeis4.)