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 A253911 #15 Sep 04 2025 21:25:13
%S A253911 12,43,65,87,911,1013,1217,1419,1523,1629,1831,2037,2141,2243,2447,
%T A253911 2553,2659,2761,2867,3071,3273,3379,3483,3589,3697,38101,39103,40107,
%U A253911 42109,44113,45127,46131,48137,49139,50149,51151,52157,54163,55167,56173,57179,58181,60191,62193,63197,64199,65211,66223,68227,69229
%N A253911 Concatenation of n-th nonprime and n-th prime.
%C A253911 Concatenate A018252(n) and A000040(n).
%H A253911 Reinhard Zumkeller, <a href="/A253911/b253911.txt">Table of n, a(n) for n = 1..10000</a>
%e A253911 a(5) = 911 because the 5th nonprime is 9 and the 5th prime is 11.
%t A253911 cncat[{a_,b_}]:=FromDigits[Flatten[IntegerDigits/@{a,b}]]; Module[ {nn=100,np,len},np = Select[Range[nn],!PrimeQ[#]&];len=Length[np];cncat/@Thread[{np,Prime[Range[len]]}]] (* _Harvey P. Dale_, Oct 17 2020 *)
%o A253911 (PARI) nprime(n)=c=0; k=1; while(k, if(!isprime(k), c++); if(c==n, return(k)); k++)
%o A253911 vector(50, n, eval(concat(Str(nprime(n)), Str(prime(n))))) \\ _Derek Orr_, Feb 06 2015
%o A253911 (Haskell)
%o A253911 import Data.Function (on)
%o A253911 a253911 n = a253911_list !! (n-1)
%o A253911 a253911_list = map read $
%o A253911 zipWith ((++) `on` show) a018252_list a000040_list :: [Integer]
%o A253911 -- _Reinhard Zumkeller_, Feb 09 2015
%Y A253911 Cf. A000040, A018252, A038530, A045532, A075110, A106582, A138821, A138822, A253910.
%K A253911 nonn,base,easy,changed
%O A253911 1,1
%A A253911 _Omar E. Pol_, Feb 06 2015