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

1,1

Links

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

Example

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

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 *)

Prog

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

Crossrefs

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

Cf. A027699 (evil primes).

Sequence in context: A090428 A039725 A262362 * A177029 A105066 A048283

Adjacent sequences: A125491 A125492 A125493 * A125495 A125496 A125497

Keyword

base,nonn

Author

Tanya Khovanova, Dec 27 2006

Extensions

Corrected and extended by Emeric Deutsch, Jan 01 2007

Status

approved