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 A053181 #19 Sep 04 2018 09:50:10 %S A053181 9,39,49,69,99,119,129,159,169,189,209,219,249,259,279,289,299,309, %T A053181 319,329,339,369,399,429,459,469,489,519,529,539,549,559,579,589,609, %U A053181 629,639,649,669,679,689,699,729,749,759,779,789,799,819,849,869,879,889,899 %N A053181 Composite numbers ending in 9. %C A053181 Numbers of the form 10n + 9 (A017377) not in A030433. Obviously multiples of 2 or 5 can't be in A017377 nor this sequence. All other primes occur as factors of these terms infinitely often. For example: If n is a multiple of 3, then 10n + 9 is in this sequence; if n = 4 mod 7, then 10n + 9 is in this sequence; if n = 9 mod 11, then 10n + 9 is in this sequence; and so on and so forth. The first of these congruences to be satisfied determines the least prime factor of 10n + 9. - _Alonso del Arte_, Jun 23 2011 %H A053181 G. C. Greubel, <a href="/A053181/b053181.txt">Table of n, a(n) for n = 1..10000</a> %F A053181 a(n) ~ 10n. - _Charles R Greathouse IV_, Jun 24 2011 %t A053181 Complement[Range[9, 1000, 10], Prime[Range[PrimePi[1000]]]] (* _Alonso del Arte_, Jun 23 2011 *) %t A053181 Select[Range[1000],CompositeQ[#]&&Mod[#,10]==9&] (* _Harvey P. Dale_, May 01 2016 *) %o A053181 (PARI) forstep(n=9,1e3,10,if(!isprime(n),print1(n", "))) \\ _Charles R Greathouse IV_, Jun 24 2011 %K A053181 easy,nonn,base %O A053181 1,1 %A A053181 _Enoch Haga_, Feb 29 2000 %E A053181 9 added by _Kausthub Gudipati_, Jun 16 2011