# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a143731 Showing 1-1 of 1 %I A143731 #15 Aug 05 2021 01:31:06 %S A143731 0,0,0,0,0,1,0,0,0,1,0,1,0,1,1,0,0,1,0,1,1,1,0,1,0,1,0,1,0,1,0,0,1,1, %T A143731 1,1,0,1,1,1,0,1,0,1,1,1,0,1,0,1,1,1,0,1,1,1,1,1,0,1,0,1,1,0,1,1,0,1, %U A143731 1,1,0,1,0,1,1,1,1,1,0,1,0,1,0,1,1,1,1 %N A143731 Characteristic function of numbers with at least two distinct prime factors (A024619). %C A143731 a(n) = 1 iff n is divisible by at least two distinct primes; otherwise 0. %H A143731 Reikku Kulon, Table of n, a(n) for n = 1..10000 %H A143731 Index entries for characteristic functions %F A143731 a(n) = abs(A079872(n)) = A057427(A079275(n)). %F A143731 For n>1: a(n) = 1 - floor(1/A001221(n)). - _Enrique Pérez Herrero_, Aug 13 2012 %t A143731 Table[Boole[PrimeNu[n]>1],{n,1,200}] (* _Enrique Pérez Herrero_, Aug 13 2012 *) %Y A143731 Cf. A024619, A079275, A079872, A000961, A001222, A091304, A073093, A001221. %Y A143731 Cf. A215480. %K A143731 easy,nonn %O A143731 1,1 %A A143731 _Reikku Kulon_, Aug 30 2008 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE