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A047932 Cumulative sum of number of new penny-penny contacts when putting pennies on a table following a spiral pattern. 4
0, 1, 3, 5, 7, 9, 12, 14, 16, 19, 21, 24, 26, 29, 31, 34, 36, 39, 42, 44, 47, 49, 52, 55, 57, 60, 63, 65, 68, 71, 73, 76, 79, 81, 84, 87, 90, 92, 95, 98, 100, 103, 106, 109, 111, 114, 117, 120, 122, 125, 128, 131, 133, 136, 139, 142, 144, 147, 150, 153, 156, 158, 161 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

This is the maximum possible number of contacts. It is also the maximum number of times the minimum distance can occur among n points in the plane.

REFERENCES

H. Harborth, Solution to problem 644A, Elemente der Mathematik (EMS Publishing House) 29, 14-15

LINKS

Peter Kagey, Table of n, a(n) for n = 1..10000

R. W. Grosse-Kunstleve, Penny Spiral Sequence [broken link]

MathOverflow, Maximal number of edges and triangular cells for n points in a triangular lattice, August 2011.

FORMULA

a(n) = floor(3*n-sqrt(12*n-3)).

MATHEMATICA

Table[Floor[3n-Sqrt[12n-3]], {n, 70}] (* Harvey P. Dale, Dec 25 2014 *)

CROSSREFS

Partial sums of A047931.

A186705 is the maximum number of times the *same* distance can occur between n points in the plane, not necessarily the *minimum*.

Sequence in context: A033036 A198082 A082767 * A139130 A219087 A186705

Adjacent sequences:  A047929 A047930 A047931 * A047933 A047934 A047935

KEYWORD

nonn

AUTHOR

Ralf W. Grosse-Kunstleve (rwgk(AT)cci.lbl.gov)

STATUS

approved

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Last modified May 30 01:26 EDT 2016. Contains 273514 sequences.