%I A090925
%S A090925 1,4,5,6,7,8,9,2,3,14,15,16,17,18,19,20,21,22,23,24,25,10,11,12,13,32,
%T A090925 33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,26,27,28,29,30,31,
%U A090925 58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80
%N A090925 Permutation of natural numbers arising from a spiral.
%C A090925 Write out the natural numbers in a square counter-clockwise spiral:
%C A090925 17.16.15.14.13
%C A090925 18..5..4..3.12
%C A090925 19..6..1..2.11
%C A090925 20..7..8..9.10
%C A090925 21.22.23.24.25
%C A090925 Now read off the numbers in a counter-clockwise spiral: 1 -> 4 -> 5 -> 
               6 -> 7 -> 8 -> 9 -> 2 -> 3 -> 14 -> etc.
%Y A090925 Sequence in context: A102691 A014553 A121855 this_sequence A143836 A089166 
               A030543
%Y A090925 Adjacent sequences: A090922 A090923 A090924 this_sequence A090926 A090927 
               A090928
%K A090925 easy,nonn
%O A090925 0,2
%A A090925 Felix Tubiana (fat2(AT)columbia.edu), Feb 26 2004