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

Author

Rémy Sigrist, Jan 30 2021

Keywords

• nonn
• look

Comments

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

Examples

			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
		

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

Crossrefs

Cf. A006530, A113552, A282291.

Programs

PARI

See Links section.