0,2

Write out the natural numbers in a square counter-clockwise spiral:

17.16.15.14.13

18..5..4..3.12

19..6..1..2.11

20..7..8..9.10

21.22.23.24.25

Now read off the numbers in a counter-clockwise spiral: 1 -> 4 -> 5 -> 6 -> 7 -> 8 -> 9 -> 2 -> 3 -> 14 -> etc.

Table of n, a(n) for n=0..71.

Sequence in context: A239440 A248355 A178053 * A143836 A168094 A089166

Adjacent sequences: A090922 A090923 A090924 * A090926 A090927 A090928

easy,nonn

Felix Tubiana (fat2(AT)columbia.edu), Feb 26 2004

approved