A338221 Square spiral of distinct positive integers built by greedy algorithm such that each new value (except the initial one) is a divisor or a multiple of some earlier horizontally or vertically adjacent value.

1, 2, 4, 3, 6, 5, 10, 7, 8, 16, 12, 20, 40, 24, 9, 18, 36, 30, 15, 45, 90, 50, 14, 28, 32, 64, 48, 60, 80, 120, 240, 160, 72, 27, 54, 108, 216, 144, 150, 25, 75, 180, 360, 270, 100, 42, 21, 63, 126, 252, 84, 96, 192, 320, 480, 720, 1440, 288, 576, 432, 81, 162

Offset

0,2

Comments

This sequence has similarities with A113552 and A282291, as each term is adjacent to one of its divisors or multiples.

Links

Rémy Sigrist, Table of n, a(n) for n = 0..10200

Rémy Sigrist, Colored representation of the spiral for -500 <= x, y <= 500 (where the color is function of a(n))

Rémy Sigrist, Colored representation of the spiral for -500 <= x, y <= 500 (where the color is function of A006530(a(n)))

Rémy Sigrist, PARI program for A338221

Example

The spiral begins:
      216--108---54---27---72--160--240
        |                             |
      144   36---18----9---24---40  120
        |    |                   |    |
      150   30    6----3----4   20   80
        |    |    |         |    |    |
       25   15    5    1----2   12   60
        |    |    |              |    |
       75   45   10----7----8---16   48
        |    |                        |
      180   90---50---14---28---32---64
        |
      360--270--100---42---21---63--126

Prog

(PARI) See Links section.

Crossrefs

Cf. A006530, A113552, A282291.

Sequence in context: A300002 A082560 A191598 * A283312 A280985 A127202

Adjacent sequences: A338218 A338219 A338220 * A338222 A338223 A338224

Keyword

nonn,look

Author

Rémy Sigrist, Jan 30 2021

Status

approved