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A130200 Evil triangular numbers. 1
3, 6, 10, 15, 36, 45, 66, 78, 105, 120, 136, 153, 190, 210, 231, 300, 325, 378, 435, 528, 561, 630, 703, 741, 780, 903, 946, 990, 1035, 1128, 1176, 1275, 1326, 1596, 1711, 1830, 1953, 2016, 2080, 2145, 2278, 2415, 2556, 2628, 2701, 2775, 2926, 3081, 3321 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..49.

FORMULA

a(n) = A130199(n)/2. Multiplying by 2 doesn't change evilness. Hence evil oblong numbers are twice evil triangular numbers.

EXAMPLE

3 belongs to the sequence because the binary expansion of 3 is 11 - contains an even number of ones.

MATHEMATICA

Select[Table[n(n + 1)/2, {n, 100}], EvenQ[Plus @@ IntegerDigits[ #, 2]] &]

CROSSREFS

Cf. This sequence is the intersection of evil numbers (A001969) and triangular numbers (A000217).

Sequence in context: A261632 A230364 A214282 * A202269 A151375 A153453

Adjacent sequences:  A130197 A130198 A130199 * A130201 A130202 A130203

KEYWORD

nonn

AUTHOR

Tanya Khovanova, May 16 2007

STATUS

approved

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Last modified April 28 16:04 EDT 2017. Contains 285578 sequences.