A360981 a(n) is the least positive multiple of n that is an evil number (A001969).

3, 6, 3, 12, 5, 6, 63, 24, 9, 10, 33, 12, 39, 126, 15, 48, 17, 18, 57, 20, 63, 66, 23, 24, 75, 78, 27, 252, 29, 30, 1023, 96, 33, 34, 105, 36, 111, 114, 39, 40, 123, 126, 43, 132, 45, 46, 141, 48, 147, 150, 51, 156, 53, 54, 165, 504, 57, 58, 177, 60, 183, 2046

Offset

1,1

Comments

This sequence is well defined: for any n > 0, A020330(n) is both a multiple of n and an evil number.

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

a(n) = A180938(n) * n.

a(n) = n iff n belongs to A001969.

Maple

f:= proc(n) local k;
  for k from n by n do
    if convert(convert(k, base, 2), `+`)::even then return k fi
  od
end proc:
map(f, [$1..100]); # Robert Israel, Mar 29 2023

Mathematica

a[n_] := Module[{k = n}, While[OddQ[DigitCount[k, 2, 1]], k +=n]; k]; Array[a, 100] (* Amiram Eldar, Aug 07 2023 *)

Prog

(PARI) a(n) = { forstep (m=n, oo, n, if (hammingweight(m)%2==0, return (m))) }
(Python)
def A360981(n):
    k = n
    while k.bit_count()&1:
        k += n
    return k # Chai Wah Wu, Feb 28 2023

Crossrefs

Cf. A001969, A020330, A180938, A360980 (variant for odious numbers).

Sequence in context: A210201 A275535 A160899 * A336769 A337035 A203491

Adjacent sequences: A360978 A360979 A360980 * A360982 A360983 A360984

Keyword

nonn,base,look

Author

Rémy Sigrist, Feb 27 2023

Status

approved