A130200 Evil triangular numbers.

0, 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

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

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, 0, 100}], EvenQ[Plus @@ IntegerDigits[ #, 2]] &]

Crossrefs

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

Sequence in context: A366132 A230364 A214282 * A202269 A151375 A353217

Adjacent sequences: A130197 A130198 A130199 * A130201 A130202 A130203

Keyword

nonn

Author

Tanya Khovanova, May 16 2007

Extensions

a(1) = 0 inserted by Amiram Eldar, Dec 09 2019

Status

approved