OFFSET
1,1
COMMENTS
Let points 2, 1, 3 & 4 be placed on a straight line at intervals of 1 unit. At point 1 make a half unit circle then at point 2 make another half circle and maintain continuity of circumferences. Continue using this procedure at point 3, 4, 1, ... and so on. The form is non-expanded loop.
The alternative point order [2, 3, 1, 4] gives the same pattern with reflection, but the sequence will be 2*A047215(n). See illustration in links.
Conjecture: Numbers equivalent 0 or 3 modulo 10. - Ralf Stephan, Jan 13 2014
LINKS
Kival Ngaokrajang, Illustration of initial terms
FORMULA
Conjecture: a(n) = -1+(-1)^n+5*n. a(n) = a(n-1)+a(n-2)-a(n-3). G.f.: x*(7*x+3) / ((x-1)^2*(x+1)). - Colin Barker, Jan 16 2014
PROG
(Small Basic)
a[1]=3
For n = 1 To 100
d1=3
If Math.Remainder(n+1, 2)=0 then
d1=7
EndIf
a[n+1]=a[n]+d1
TextWindow.Write(a[n]+", ")
EndFor
CROSSREFS
KEYWORD
nonn
AUTHOR
Kival Ngaokrajang, Jan 03 2014
STATUS
approved