(Translated by https://www.hiragana.jp/)
# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a066899 Showing 1-1 of 1 %I A066899 #21 Feb 23 2021 05:25:38 %S A066899 1,3,1,4,2,5,1,7,2,3,2,7,2,5,2,7,2,5,2,10,2,3,3,15,2,3,2,5,3,3,1,12,4, %T A066899 5,2,9,2,7,2,12,3,7,2,8,4,3,2,16,2,5,3,4,4,9,2,10,2,3,4,12,2,5,2,15,3, %U A066899 3,2,9,5,5,2,20,2,5,3,8,3,5,2,15,2,3,5,12,2 %N A066899 a(n) = card({k : phi(k) == n (mod k)}). %C A066899 Note that k=1 is excluded from the count. - _Michel Marcus_, Feb 22 2021 %H A066899 Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems: invphi.gp, 2005-2019. %o A066899 (PARI) a(n) = {my(v = invphi(n), m = if (#v, vecmax(v), n)); sum(i=2, m, Mod(eulerphi(i), i) == n);} \\ _Michel Marcus_, Feb 22 2021; needs invphi.gp %Y A066899 Cf. A000010, A014197, A066900. %K A066899 nonn %O A066899 1,2 %A A066899 _Benoit Cloitre_, Jan 24 2002 %E A066899 More terms from _Michel Marcus_, Feb 22 2021 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE