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 A049852 #25 Nov 20 2019 12:13:14 %S A049852 12,23,35,45,57,67,711,811,911,1011,1113,1213,1317,1417,1517,1617, %T A049852 1719,1819,1923,2023,2123,2223,2329,2429,2529,2629,2729,2829,2931, %U A049852 3031,3137,3237,3337,3437,3537,3637,3741,3841,3941,4041,4143,4243 %N A049852 Concatenate "n" and "nextprime(n)". %C A049852 From _Petros Hadjicostas_, Nov 20 2019: (Start) %C A049852 Version 1 of the "next prime" function is A007918: smallest prime >= n. PARI/GP's nextprime() is version 1. %C A049852 Maple's nextprime() is the version 2 that appears in A151800: smallest prime > n. We use version 2 here. (End) %e A049852 From _Petros Hadjicostas_, Nov 20 2019: (Start) %e A049852 a(1) = 12 because nextprime(1) = 2. %e A049852 a(2) = 23 because nextprime(2) = 3. %e A049852 a(3) = 35 because nextprime(3) = 5. %e A049852 a(4) = 45 because nextprime(4) = 5. %e A049852 ... %e A049852 a(10) = 1011 because nextprime(10) = 11. %e A049852 a(11) = 1113 because nextprime(11) = 13. %e A049852 ... (End) %p A049852 a:= n-> parse(cat(n, nextprime(n))): %p A049852 seq(a(n), n=1..50); # _Alois P. Heinz_, Nov 20 2019 %o A049852 (PARI) a(n) = eval(concat(Str(n), Str(nextprime(n+1)))); \\ _Michel Marcus_, Jan 01 2017 %Y A049852 Cf. A007918 (version 1 of nextprime), A151800 (version 2 of nextprime). %K A049852 nonn,base %O A049852 1,1 %A A049852 _N. J. A. Sloane_