This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A103899 #33 Oct 08 2014 17:03:13
%S A103899 2,1,1,2,1,50,2,13,10
%N A103899 Concatenation of next a(n) odd numbers is prime.
%C A103899 From _Vladimir Shevelev_ and _Peter J. C. Moses_, Sep 30 2014: (Start)
%C A103899 Consider a partition of consecutive odd numbers in minimal blocks such that concatenation of numbers in each block is a prime. The sequence lists the numbers of odd numbers in each block.
%C A103899 The first blocks are |1,3|5|7|9,11|13|15,17,...,111,113|115,117|, etc.
%C A103899 The prime corresponding to a(6) has 107 digits; a(10) has more than 58759 digits.
%C A103899 (End)
%e A103899 a(1)=2 because 13 is prime.
%e A103899 Then we have p(2)=5, p(3)=7, p(4)=911, p(5)=13. The primes obtained for n=7 to 9 are: 115117, 119121123125127129131133135137139141143, 145147149151153155157159161163. The next prime to find should begin with "165". Next term a(10), if it exists, is > 1000. - _Michel Marcus_, Oct 05 2013
%t A103899 c = 1; Do[p = c; k = 1; While[ !PrimeQ[p], c += 2; p = p*10^Length[IntegerDigits[c]] + c; k++ ]; Print[k]; c += 2, {n, 1, 30}] (* _Ryan Propper_, Aug 10 2005 *)
%o A103899 (PARI) findn(n) = {new = n; conc = n; while (! isprime(conc), new += 2; conc = eval(concat(Str(conc), Str(new)));); print1(conc, ", "); new+2;}
%o A103899 lista(nn) = {odd = 1; for (i = 1, nn, nodd = findn(odd); nb = (nodd - odd)/2; print1(nb, ", "); odd = nodd; print("new odd ", odd););} \\ _Michel Marcus_, Oct 05 2013
%K A103899 nonn,base,more
%O A103899 1,1
%A A103899 _Zak Seidov_, Mar 30 2005
%E A103899 4 more terms from _Ryan Propper_, Aug 10 2005