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 A071601 #15 Jun 28 2022 02:50:31 %S A071601 1,2,4,8,9,16,18,32,33,36,49,64,65,66,69,72,77,98,99,121,128,130,132, %T A071601 138,141,144,145,154,169,177,196,198,209,225,242,256,260,261,264,265, %U A071601 276,282,288,290,297,305,308,325,338,354,361,392,396,418,441,450,484 %N A071601 Numbers k such that k and phi(k) have the same number of 1's in their binary representation. %H A071601 Amiram Eldar, <a href="/A071601/b071601.txt">Table of n, a(n) for n = 1..10000</a> %e A071601 676 = 1010100100 in base 2, phi(676) = 312 = 100111000 in base 2, hence 676 is in the sequence. %t A071601 Select[Range[500],DigitCount[#,2,1]==DigitCount[EulerPhi[#],2,1]&] (* _Harvey P. Dale_, Jun 17 2021 *) %o A071601 (PARI) for(n=1,1000,if(sum(i=1,length(binary(n)), component(binary(n),i))==sum(i=1,length(binary(eulerphi(n))), component(binary(eulerphi(n)),i)),print1(n,","))) %Y A071601 Cf. A000010, A000120, A295660. %K A071601 base,easy,nonn %O A071601 1,2 %A A071601 _Benoit Cloitre_, Jun 01 2002