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