A049317 Number of 3-dimensional integer direction vectors (a,b,c) towards grid points at squared integer distance 2n-1 with a >= b >= c >= 0.

1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 4, 3, 3, 5, 4, 4, 7, 4, 5, 6, 6, 6, 6, 6, 7, 9, 7, 6, 11, 8, 8, 12, 7, 9, 12, 9, 10, 10, 12, 10, 14, 11, 9, 14, 12, 12, 16, 10, 13, 19, 13, 13, 16, 14, 14, 18, 15, 12, 18, 16, 17, 21, 13, 16, 23, 17, 20, 18, 18, 18, 24, 18, 15, 28, 19, 19, 25

Offset

1,5

Comments

A vector is a direction vector if its nonzero components have their GCD = 1.

Links

Table of n, a(n) for n=1..77.

Example

The 4 directions towards points at squared distance 29 (i.e. for n=15) are (signed permutations of) [ 24,16,3 ],[ 24,12,11 ],[ 21,20,0 ],[ 21,16,12 ]

Crossrefs

Cf. A049318, A049319.

Sequence in context: A288157 A333701 A140682 * A134544 A230514 A106161

Adjacent sequences: A049314 A049315 A049316 * A049318 A049319 A049320

Keyword

nonn

Author

Wouter Meeussen

Status

approved