Search: id:A140222
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%I A140222
%S A140222 2,3,9,11,13,14,28,29,31,34,35,51,54,56,61,81,83,93,94,97,98,123,124,
%T A140222 131,140,142,171,173,177,179,180,185,187,190,191,193,195,228,230,231,
%U A140222 233,234,248,251,290,293,294,296,297,304,309,310,315,316,320,322,373
%N A140222 A number n is included if (sum{k=1 to n} d(k)) is prime, where d(k) is 
               the number of divisors of k.
%C A140222 sum{k=1 to n} d(k) = sum{k=1 to n} floor(n/k) = A006218(n).
%H A140222 Leroy Quet, <a href="http://www.prism-of-spirals.net/">Home Page</a> 
               (listed in lieu of email address)
%e A140222 9 is in the sequence because the number of divisors of 1,2,...,9 are 
               1,2,2,3,2,4,2,4,3, respectively, having as sum the prime number 23.
%p A140222 with(numtheory): a:=proc(n) if isprime(sum(tau(k),k=1..n))=true then 
               n else end if end proc: seq(a(n),n=1..400); - Emeric Deutsch (deutsch(AT)duke.poly.edu), 
               Jun 08 2008
%Y A140222 Cf. A006218, A140221.
%Y A140222 Sequence in context: A057236 A063257 A103039 this_sequence A121557 A138984 
               A110772
%Y A140222 Adjacent sequences: A140219 A140220 A140221 this_sequence A140223 A140224 
               A140225
%K A140222 nonn
%O A140222 1,1
%A A140222 Leroy Quet May 12 2008
%E A140222 More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Jun 08 2008

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