Search: id:A089821
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%I A089821
%S A089821 0,2,4,8,12,24,32,64,128,256,320,640,768,1536,3072,6144,7168,14336,
%T A089821 16384,32768,65536,131072,147456,294912,589824,1179648,2359296,4718592,
%U A089821 5242880,10485760,11534336,23068672,46137344,92274688
%N A089821 Number of subsets of {1,.., n} containing exactly one prime.
%C A089821 a(n )= A000720(n)*A089819(n);
%C A089821 for n>1: a(n) = A089818(n,1).
%F A089821 a(n) = pi(n) * 2^(n-pi(n)), with pi = A000720.
%e A089821 a(5)=12 subsets of {1,2,3,4,5} contain exactly one prime: {2},
%e A089821 {3}, {5}, {1,2}, {1,3}, {1,5}, {2,4}, {3,4}, {4,5}, {1,2,4}, {1,3,4} 
               and {1,4,5}.
%Y A089821 Cf. A089822.
%Y A089821 Sequence in context: A103787 A032473 A084422 this_sequence A097942 A004653 
               A115386
%Y A089821 Adjacent sequences: A089818 A089819 A089820 this_sequence A089822 A089823 
               A089824
%K A089821 nonn
%O A089821 1,2
%A A089821 Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Nov 12 2003

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