Search: id:A130200
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%I A130200
%S A130200 3,6,10,15,36,45,66,78,105,120,136,153,190,210,231,300,325,378,435,528,
%T A130200 561,630,703,741,780,903,946,990,1035,1128,1176,1275,1326,1596,1711,
%U A130200 1830,1953,2016,2080,2145,2278,2415,2556,2628,2701,2775,2926,3081,3321
%N A130200 Evil triangular numbers.
%F A130200 a(n) = A130199(n)/2. Multiplying by 2 doesn't change evilness. Hence 
               evil oblong numbers are twice evil triangular numbers.
%e A130200 3 belongs to the sequence because the binary expansion of 3 is 11 - contains 
               an even number of ones.
%t A130200 Select[Table[n(n + 1)/2, {n, 100}], EvenQ[Plus @@ IntegerDigits[ #, 2]] 
               &]
%Y A130200 Cf. This sequence is the intersection of evil numbers (A001969) and triangular 
               numbers (A000217).
%Y A130200 Sequence in context: A024674 A026104 A058576 this_sequence A151375 A153453 
               A025215
%Y A130200 Adjacent sequences: A130197 A130198 A130199 this_sequence A130201 A130202 
               A130203
%K A130200 nonn
%O A130200 1,1
%A A130200 Tanya Khovanova (tanyakh(AT)yahoo.com), May 16 2007

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