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 A275319 #8 Sep 08 2022 08:46:17 %S A275319 1,3,4,5,7,9,10,11,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29, %T A275319 30,31,32,33,34,35,37,38,39,40,41,43,44,45,46,47,48,49,51,52,53,54,55, %U A275319 57,58,59,60,61,63,64,65,66,67,69,70,71,72,73,74,75,76 %N A275319 Numbers n such that n concatenated with n+1 is not a prime. %C A275319 Complement of A030457. %C A275319 Conjecture: a(n) ~ n. - _Charles R Greathouse IV_, Jul 23 2016 %H A275319 Charles R Greathouse IV, <a href="/A275319/b275319.txt">Table of n, a(n) for n = 1..10000</a> %t A275319 Select[Range[100], !PrimeQ[FromDigits[Join[IntegerDigits[#], IntegerDigits[# + 1]]]] &] %o A275319 (Magma) [n: n in [1..500] | not IsPrime(Seqint(Intseq(n+1) cat Intseq(n)))] %o A275319 (PARI) is(n)=!isprime(eval(Str(n,n+1))) \\ _Charles R Greathouse IV_, Jul 23 2016 %Y A275319 Cf. A030457. %K A275319 nonn,easy,base %O A275319 1,2 %A A275319 _Vincenzo Librandi_, Jul 23 2016