A130199 - OEIS

%I #8 Mar 16 2022 21:01:39

%S 0,6,12,20,30,72,90,132,156,210,240,272,306,380,420,462,600,650,756,

%T 870,1056,1122,1260,1406,1482,1560,1806,1892,1980,2070,2256,2352,2550,

%U 2652,3192,3422,3660,3906,4032,4160,4290,4556,4830,5112,5256,5402,5550,5852

%N Evil oblong (promic) numbers.

%H Amiram Eldar, <a href="/A130199/b130199.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = 2*A130200(n). Multiplying by 2 doesn't change evilness. Hence evil oblong numbers are twice evil triangular numbers.

%e 6 belongs to the sequence because binary expansion of 6 is 110 - contains an even number of ones.

%t Select[Table[n(n + 1), {n, 0, 100}], EvenQ[Plus @@ IntegerDigits[ #, 2]] &]

%o (PARI) is(n)=n%2==0 && hammingweight(n)%2==0 && ispolygonal(n/2,3) \\ _Charles R Greathouse IV_, Mar 16 2022

%Y Cf. This sequence is the intersection of evil numbers (A001969) and oblong numbers (A002378).

%K nonn,easy

%O 1,2

%A _Tanya Khovanova_, May 16 2007

%E a(1) = 0 inserted and offset corrected by _Amiram Eldar_, Dec 09 2019