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 A281685 #12 Apr 23 2017 23:59:34 %S A281685 4,16,18,20,21,24,26,27,33,35,38,40,44,45,48,50,51,52,56,57,62,63,65, %T A281685 68,69,74,75,76,77,80,85,86,91,92,93,95,96,98,99,104,106,108,111,115, %U A281685 117,119,122,123,126,129,133,134,135,136,141,143,144,145,146,147 %N A281685 Numbers k such that A001221(k) = A001221(A003415(k)). %C A281685 Numbers k such that the number of distinct prime divisors of k is equal to the number of distinct prime divisors of the arithmetic derivative of k. %H A281685 Colin Barker, <a href="/A281685/b281685.txt">Table of n, a(n) for n = 1..1000</a> %t A281685 a[n_] := If[Abs@n < 2, 0, n Total[#2/#1 & @@@ FactorInteger[Abs@n]]]; %t A281685 Select[Range[100], PrimeNu[#] == PrimeNu[a[#]] &] (* _G. C. Greubel_, Apr 23 2017 *) %o A281685 (PARI) arde(n) = sum(i=1, #f=factor(n)~, n/f[1, i]*f[2, i]) %o A281685 select(k->omega(k)==omega(arde(k)), vector(200, k, k+1)) %Y A281685 Cf. A001221, A003415, A209870, A281686. %K A281685 nonn %O A281685 1,1 %A A281685 _Colin Barker_, Jan 27 2017