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 A109369 #15 Sep 08 2022 08:45:19 %S A109369 1,7,13,19,23,29,31,43,47,59,61,71,73,89,91,107,113,119,149,151,161, %T A109369 179,181,191,199,203,211,223,247,287,289,301,311,317,329,331,343,347, %U A109369 349,353,359,377,391,403,409,413,427,457,461,469,479,487,493,503,521 %N A109369 Numbers n such that the string 33n is the decimal expansion of a prime number. %H A109369 Vincenzo Librandi, <a href="/A109369/b109369.txt">Table of n, a(n) for n = 1..2000</a> %e A109369 1 is in the sequence because 331 is prime. %e A109369 59 is in the sequence because 3359 is prime. %e A109369 107 is in the sequence because 33107 is prime. %p A109369 a:=proc(n) if isprime(33*10^nops(convert(n,base,10))+n)=true then n else fi end: seq(a(n),n=0..600); # _Emeric Deutsch_, Sep 02 2005 %t A109369 Select[Range[600],PrimeQ[33*10^IntegerLength[#]+#]&] (* _Harvey P. Dale_, Jul 29 2014 *) %o A109369 (Magma) [ n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [3, 3])) ]; %K A109369 nonn,base %O A109369 1,2 %A A109369 _Parthasarathy Nambi_, Aug 24 2005 %E A109369 More terms from _Emeric Deutsch_, Sep 02 2005