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 A089987 #43 Nov 05 2018 21:07:49
%S A089987 2,23,23456789,23456789101112131415161718192021222324252627
%N A089987 Primes in the concatenation of consecutive numbers beginning with 2.
%C A089987 Sum of reciprocals = 0.5434783035011462065880780409...
%C A089987 23, 4567 and 89 are prime numbers, thus a(3) = A262571(9) = 23456789 is a prime obtained by concatenating 3 primes that are themselves the concatenation of consecutive integers. - _XU Pingya_, Apr 16 2017
%C A089987 No other primes less than the concatenation of 2,3,4,5,6,7,8,9,10,11,12,...,9999. - _Robert Price_, Nov 04 2018
%t A089987 Select[Table[FromDigits[Flatten[IntegerDigits[Range[2, n]]]], {n, 2, 30}], PrimeQ[#] & ] (* _Robert Price_, Nov 05 2018 *)
%o A089987 (PARI) concatprime(n,p) = { sr=0; y=""; for(x=p,n, y=concat(Str(y),Str(x)); z=eval(y); if(ispseudoprime(z),print1(z","); sr+=1./z; ); ); print(); print(sr) }
%Y A089987 Primes in A262571.
%Y A089987 See A262300 for more information.
%Y A089987 See also A007908 for the numbers 1234...n.
%K A089987 nonn,base,more
%O A089987 1,1
%A A089987 _Cino Hilliard_, Jan 14 2004
%E A089987 Offset corrected by _Michel Marcus_, Apr 21 2017