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A262552 Numbers n such that the concatenation of the decimal numbers 1 through n, but omitting 5, is a prime. 2

%I

%S 11,17,157,3631

%N Numbers n such that the concatenation of the decimal numbers 1 through n, but omitting 5, is a prime.

%C The corresponding primes are the primes in A262575.

%C The actual values of a(1) to a(4) are also primes, although that is not a necessary condition for a number to belong to this sequence. Not all the terms of A262300 are primes, for example.

%C Probabilistic arguments suggest the sequence is infinite.

%C a(5) > 10000. - _Robert Price_, Nov 03 2018

%e The first two terms correspond to the primes 123467891011 and 123467891011121314151617.

%e a(3) corresponds to a 362-digit prime, a(4) to a 13416-digit probable prime. These two terms were found by _David Broadhurst_ on Oct 08 2015.

%Y Cf. A262575, A262300, A007908.

%K nonn,base,more

%O 1,1

%A _N. J. A. Sloane_, Oct 09 2015

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Last modified June 21 03:24 EDT 2021. Contains 345354 sequences. (Running on oeis4.)