A262299 - OEIS

A262299

Let S(n) denote the sequence formed by concatenating the decimal numbers 1,2,3,..., omitting n; a(n) is the smallest prime in S(n), or -1 if no term in S(n) is prime.

%I #30 Sep 29 2015 09:15:54

%S 2,13,124567,12356789,123467891011,123457,123456891011

%N Let S(n) denote the sequence formed by concatenating the decimal numbers 1,2,3,..., omitting n; a(n) is the smallest prime in S(n), or -1 if no term in S(n) is prime.

%C A262300 is now the main entry for this question.

%e a(8) = 1234567910111213...1873 (ending at 1873, a 6384-digit probable prime, and too large to display here) was found by _David Broadhurst_ on Sep 27 2015.

%e a(9) = 1234567810111213141516171819,

%e a(11) = 123456789101213,

%e and a(19) = 12345678910111213141516171820212223242526272829.

%e Sep 28, 2015: _David Broadhurst_ has also found a(10), a(12), a(14), a(16), a(17), a(18), and a(20). See A262300 for their values.

%e a(13) is at present unknown.

%Y A262300 gives the last term in S(n) when a prime appears for the first time.

%Y See A262571-A262582 for the sequences S(1) through S(12).

%Y Cf. A007908 (which plays the role of S(0)).

%Y For the primes in S(1) and S(2) see A089987, A262298.

%K nonn,base,more

%O 1,1

%A _N. J. A. Sloane_ and Jerrold B. Tunnell, Sep 25 2015