A047931 Number of new penny-penny contacts when putting pennies on a table following a spiral pattern.

0, 1, 2, 2, 2, 2, 3, 2, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 3, 2, 3, 2, 3, 3, 2, 3, 3, 2, 3, 3, 2, 3, 3, 2, 3, 3, 3, 2, 3, 3, 2, 3, 3, 3, 2, 3, 3, 3, 2, 3, 3, 3, 2, 3, 3, 3, 2, 3, 3, 3, 3, 2, 3, 3, 3, 2, 3, 3, 3, 3, 2, 3, 3, 3, 3, 2, 3, 3, 3, 3, 2, 3, 3, 3, 3, 2, 3, 3, 3, 3, 3

Offset: 1

Author

Ralf W. Grosse-Kunstleve

Keywords

• nonn

Examples

			From _Omar E. Pol_, Nov 16 2016: (Start)
The sequence written as a spiral begins:
.
.                2 - 3 - 3 - 3 - 3 - 2
.               /                     \
.              3   2 - 3 - 3 - 3 - 2   3
.             /   /                 \   \
.            3   3   2 - 3 - 3 - 2   3   3
.           /   /   /             \   \   \
.          3   3   3   2 - 3 - 2   3   3   3
.         /   /   /   /         \   \   \   \
.        3   3   3   3   2 - 2   3   3   3   3
.       /   /   /   /   /     \   \   \   \   \
.      2   2   2   2   2   0 - 1   2   2   2   2
.       \   \   \   \   \         /   /   /   /
.        3   3   3   3   2 - 3 - 2   3   3   3
.         \   \   \   \             /   /   /
.          3   3   3   2 - 3 - 3 - 2   3   3
.           \   \   \                 /   /
.            3   3   2 - 3 - 3 - 3 - 2   3
.             \   \                     /
.              3   2 - 3 - 3 - 3 - 3 - 2
.               \
.                2 - 3 - 3 - 3 - 3 - 3
(End)
		

Links

• R. W. Grosse-Kunstleve, Penny Spiral Sequence

Crossrefs

Cf. A047932.

Formula

The n-th "chunk" consists of 2 3{n-2} 2 3{n-1} 2 3{n-1} 2 3{n-1} 2 3{n-1} 2 3{n}, where a{b} symbolizes b repetitions of a.