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%I #6 Dec 09 2019 09:21:09
%S 0,3,6,10,15,36,45,66,78,105,120,136,153,190,210,231,300,325,378,435,
%T 528,561,630,703,741,780,903,946,990,1035,1128,1176,1275,1326,1596,
%U 1711,1830,1953,2016,2080,2145,2278,2415,2556,2628,2701,2775,2926,3081,3321
%N Evil triangular numbers.
%H Amiram Eldar, <a href="/A130200/b130200.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = A130199(n)/2. Multiplying by 2 doesn't change evilness. Hence evil oblong numbers are twice evil triangular numbers.
%e 3 belongs to the sequence because the binary expansion of 3 is 11 - contains an even number of ones.
%t Select[Table[n(n + 1)/2, {n, 0, 100}], EvenQ[Plus @@ IntegerDigits[ #, 2]] &]
%Y Cf. This sequence is the intersection of evil numbers (A001969) and triangular numbers (A000217).
%K nonn
%O 1,2
%A _Tanya Khovanova_, May 16 2007
%E a(1) = 0 inserted by _Amiram Eldar_, Dec 09 2019
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