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 A045590 #25 May 22 2025 00:59:33 %S A045590 1,3,9,21,27,63,81,147,189,243,441,567,729,903,1029,1323,1701,2187, %T A045590 2667,2709,2943,3087,3969,5103,6321,6561,7203,8001,8127,8829,9261, %U A045590 11907,13203,15309,18669,18963,19683,20601,21609,24003,24381,26487 %N A045590 Numbers k that divide 5^k + 4^k. %C A045590 From _Robert Israel_, May 19 2025: (Start) %C A045590 All terms are coprime to 10. %C A045590 The only prime term is 3. %C A045590 If k is a term, then so is 3 * k. %C A045590 Is 1 the only term not divisible by 3? (End) %H A045590 Robert Israel, <a href="/A045590/b045590.txt">Table of n, a(n) for n = 1..1000</a> %p A045590 filter:= k -> 5 &^ k + 4 &^ k mod k = 0: %p A045590 select(filter, [seq(i,i=1..10^5,2)]); # _Robert Israel_, May 19 2025 %t A045590 Select[Range[30000],Divisible[5^#+4^#,#]&] (* _Harvey P. Dale_, Nov 17 2013 *) %Y A045590 Cf. A074611. %K A045590 nonn %O A045590 1,2 %A A045590 _David W. Wilson_