A125494 Composite evil numbers.

6, 9, 10, 12, 15, 18, 20, 24, 27, 30, 33, 34, 36, 39, 40, 45, 46, 48, 51, 54, 57, 58, 60, 63, 65, 66, 68, 72, 75, 77, 78, 80, 85, 86, 90, 92, 95, 96, 99, 102, 105, 106, 108, 111, 114, 116, 119, 120, 123, 125, 126, 129, 130, 132, 135, 136, 141, 142, 144, 147, 150, 153

Offset: 1

Author

Tanya Khovanova, Dec 27 2006

Keywords

• base
• nonn

Examples

			12 is in the sequence since it is composite and its base-2 representation (1100) has an even number of 1's.
		

Links

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

Crossrefs

Intersection of A002808 (composite numbers) and A001969 (evil numbers).

Cf. A027699 (evil primes).

Programs

Maple

a:=proc(n) local n2: n2:=convert(n,base,2): if add(n2[j],j=1..nops(n2)) mod 2 = 0 and isprime(n)=false then n else fi end: seq(a(n),n=1..180); # Emeric Deutsch, Jan 01 2007

Mathematica

Select[Range[153], EvenQ @ DigitCount[#, 2][[1]] && CompositeQ[#] &] (* Amiram Eldar, Dec 09 2019 *)

PARI

isok(n) = (n>0) && !isprime(n) && !(hammingweight(n) % 2); \\ Michel Marcus, Mar 29 2019

Extensions

Corrected and extended by Emeric Deutsch, Jan 01 2007