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 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

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Last modified May 30 18:48 EDT 2024. Contains 372974 sequences. (Running on oeis4.)