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 A053574 #31 Sep 05 2023 01:42:34 %S A053574 0,0,1,1,2,1,1,2,1,2,1,2,2,1,3,3,4,1,1,3,2,1,1,3,2,2,1,2,2,3,1,4,2,4, %T A053574 3,2,2,1,3,4,3,2,1,2,3,1,1,4,1,2,5,3,2,1,3,3,2,2,1,4,2,1,2,5,4,2,1,5, %U A053574 2,3,1,3,3,2,3,2,2,3,1,5,1,3,1,3,6,1,3,3,3,3,3,2,2,1,3,5,5,1,2,3,2,5,1,4,4,2,1,2,2,3,3,4,4,2,3,3,3,1,5,5 %N A053574 Exponent of 2 in phi(n) where phi(n) = A000010(n). %H A053574 Antti Karttunen, <a href="/A053574/b053574.txt">Table of n, a(n) for n = 1..10000</a> %F A053574 a(n) = A007814(A000010(n)). %F A053574 A000010(n) = A053575(n) * 2^a(n). - _Antti Karttunen_, May 26 2017 %F A053574 Additive with a(2^e) = e-1, and a(p^e) = A007814(p-1) for an odd prime p. - _Amiram Eldar_, Sep 05 2023 %e A053574 For n = 513 = 27*19, phi(513) = 4*81 so exponent of 2 is 2, thus a(513) = 2. %t A053574 IntegerExponent[Array[EulerPhi, 120], 2] (* _Michael De Vlieger_, Aug 16 2017 *) %o A053574 (PARI) vector(66,n,valuation(eulerphi(n),2)) \\ _Joerg Arndt_, Apr 22 2011 %Y A053574 Cf. A000010, A007814, A053575, A286572. %K A053574 nonn,easy %O A053574 1,5 %A A053574 _Labos Elemer_, Jan 18 2000 %E A053574 Data section extended to 120 terms by _Antti Karttunen_, May 26 2017