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 A032621 #15 May 13 2025 11:33:53 %S A032621 1,11,13,17,25,31,35,43,65,71,83,95,97,101,125,127,137,151,155,157, %T A032621 161,163,167,187,197,203,205,211,217,221,223,227,233,235,245,251,257, %U A032621 263,265,271,283,317,331,335,337,341,353,355,373,385,391,401,427,433 %N A032621 Numbers k such that k concatenated with k+6 is a prime. %H A032621 Robert Israel, <a href="/A032621/b032621.txt">Table of n, a(n) for n = 1..10000</a> %p A032621 filter:= n -> isprime(n * 10^(1+ilog10(n+6)) + n + 6): %p A032621 select(filter, [seq(i,i=1..1000,2)]); # _Robert Israel_, May 13 2025 %t A032621 Select[Range[1,501,2],PrimeQ[FromDigits[Join[IntegerDigits[#], IntegerDigits[ #+6]]]]&] (* _Harvey P. Dale_, Nov 17 2013 *) %Y A032621 Cf. A032611. %K A032621 nonn,base %O A032621 1,2 %A A032621 _Patrick De Geest_, May 15 1998