login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A242395 Number of equilateral triangles (sides length = 1) that intersect the circumference of a circle of radius n centered at (1/2,0). 4
14, 26, 38, 58, 70, 82, 98, 110, 122, 142, 154, 166, 182, 194, 206, 218, 238, 250, 262, 278, 290, 302, 322, 334, 346, 362, 374, 386, 398, 418, 430, 442, 458, 470, 482, 502, 514, 526, 542, 554, 566, 578, 598, 610, 622, 638, 650, 662, 682, 694, 706, 722, 734, 746, 766, 778, 790 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For all n, it seems to be the case that transits of the circumference occurring exactly at the corners do not exist. The pattern repeats itself at a half circle. The triangle count in a quadrant by rows can be arranged as an irregular triangle as shown in the illustration. The rows count (A242396) is equal to the case centered at (0,0), A242394.

LINKS

Table of n, a(n) for n=1..57.

Kival Ngaokrajang, Illustration of initial terms

PROG

(Small Basic)

a[0]=3

iy=0

For n = 1 To 100

   r=n/(math.Power(3, 0.5)/2)

   If r-math.Floor(r)>=0.5 Then

     ix=1

   Else

     ix=0

   EndIf

   If n=1 Then

     d1=0

   Else

     If ix=iy Then

       d1=3

     Else

       if ix=1 and iy=0 Then

         d1=5

       Else

         d1=4

       EndIf

     EndIf

   EndIf

   iy=ix

   a[n]=a[n-1]+d1

   TextWindow.Write(2*(2*a[n]+1)+", ")

EndFor

CROSSREFS

Cf. A242118.

Sequence in context: A240227 A191992 A082773 * A112772 A155505 A086258

Adjacent sequences:  A242392 A242393 A242394 * A242396 A242397 A242398

KEYWORD

nonn

AUTHOR

Kival Ngaokrajang, May 13 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 13 23:41 EDT 2021. Contains 343868 sequences. (Running on oeis4.)