cp's OEIS Frontend

A179890 Values of antiharmonic mean B(q) of the numbers k < q such that gcd(k, q) = 1 is an integer for nonprimes q from A179887, where B(q) = A053818(q) / A023896(q) = A175505(q) / A175506(q).

%I A179890 #25 May 26 2025 09:54:48
%S A179890 1,7,15,23,31,37,39,55,57,61,63,71,73,77,79,89,95,97,111,113,119,121,
%T A179890 125,135,137,143,145,151,153,157,165,169,173,175,177,177,183,193,197,
%U A179890 199,201,213,223,231,237,239,249,255,261,263,269,273,277,285,289,297,301,303,303
%N A179890 Values of antiharmonic mean B(q) of the numbers k < q such that gcd(k, q) = 1 is an integer for nonprimes q from A179887, where B(q) = A053818(q) / A023896(q) = A175505(q) / A175506(q).
%H A179890 Amiram Eldar, <a href="/A179890/b179890.txt">Table of n, a(n) for n = 1..10000</a>
%e A179890 a(6) = 37 because for A179887(6) = 55 holds: B(55) = A053818(55)/A023896(55) = 40700/1100 = 37.
%o A179890 (PARI) list(lim) = print1(1, ", "); for(k = 2, lim, if(!isprime(k), my(f = factor(k), b = 2*k/3 + (1/3) * prod(i = 1, #f~, 1 - f[i, 1])/eulerphi(f)); if(denominator(b) == 1, print1(b, ", ")))); \\ _Amiram Eldar_, May 26 2025
%Y A179890 Cf. A023896, A053818, A175505, A175506.
%Y A179890 Cf. A179871, A179872, A179873, A179874, A179875, A179876, A179877, A179878, A179879, A179880, A179882, A179883, A179884, A179885, A179886, A179887, A179890, A179891.
%K A179890 nonn
%O A179890 1,2
%A A179890 _Jaroslav Krizek_, Jul 30 2010, Jul 31 2010
%E A179890 Incorrect formula removed by _Amiram Eldar_, May 26 2025