A378541 Practical numbers whose sum of divisors is even.

6, 12, 20, 24, 28, 30, 40, 42, 48, 54, 56, 60, 66, 78, 80, 84, 88, 90, 96, 104, 108, 112, 120, 126, 132, 140, 150, 156, 160, 168, 176, 180, 192, 198, 204, 208, 210, 216, 220, 224, 228, 234, 240, 252, 260, 264, 270, 272, 276, 280, 294, 300, 304, 306, 308, 312, 320, 330, 336, 340, 342, 348, 352, 360, 364, 368, 378, 380

Offset

1,1

Comments

Practical numbers without any squares or twice squares.

Links

Antti Karttunen, Table of n, a(n) for n = 1..10000

Example

20 is in the sequence as it is practical (every number from 1 through sigma(20) = 42 can be written as the sum of some distinct divisors of 20) and sigma(20) = 42 is even.
21 is not in the sequence as it is not practical.

Prog

(PARI) isA378541 = A378540;

Crossrefs

Intersection of A005153 and A028983.

Setwise difference A083207 \ A353061.

Cf. A378540 (characteristic function).

Sequence in context: A345919 A246198 A083207 * A378599 A370205 A304391

Adjacent sequences: A378538 A378539 A378540 * A378542 A378543 A378544

Keyword

nonn,new

Author

Antti Karttunen and David A. Corneth, Dec 02 2024

Status

approved