

A229593


Number of boomerang patterns appearing in n X n coins, rotation not allowed.


12



0, 2, 3, 4, 10, 12, 14, 24, 27, 30, 44, 48, 52, 70, 75, 80, 102, 108, 114, 140, 147, 154, 184, 192, 200, 234, 243, 252, 290, 300, 310, 352, 363, 374, 420, 432, 444, 494, 507, 520, 574, 588, 602, 660, 675, 690, 752, 768
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OFFSET

2,2


COMMENTS

The boomerang pattern is one of a total of 17 distinct patterns appearing in a 3 X 2 rectangular array of coins where each pattern consists of perimeter parts from each of 6 coins and forms a continuous area. See illustration of 6curve patterns in links.
a(n) is the number of boomerang patterns appearing in an n X n array of coins with rotation not allowed. The number of inverse patterns is given in A229598.
It appears that a(n+1) is equivalent to n multiplied by the least possible number of addends in the partition in which the addends are multiplied together to produce the largest possible product for all n > 2. E.g., in the case of a(11), we look for partitions of 10, and for each partition we take the product of all its addends. The largest possible product formed is 3*3*2*2 = 3*3*4 = 36. The least possible number of addends here is 3, which we multiply by 10 to get 30.  Laurance L. Y. Lau, Jun 22 2015


LINKS



FORMULA

G.f.: (2*x^6 + x^5 + x^4 + 2*x^3)/((1x^3)^2 * (1x)).  Ralf Stephan, Oct 05 2013


MATHEMATICA

CoefficientList[Series[(2 x^4 + x^3 + x^2 + 2 x)/((1  x^3)^2 (1  x)), {x, 0, 80}], x] (* Vincenzo Librandi, Oct 10 2013 *)


PROG

(Small Basic)
b[2]=0
d[3]=2
d[4]=1
d[5]=1
For n=2 To 100
If n+1 >=6 Then
If Math.Remainder(n+1, 3)=0 Then
d[n+1]=d[n2]+4
Else
d[n+1]=d[n2]+1
EndIf
EndIf
b[n+1]=b[n]+d[n+1]
TextWindow.Write(b[n]+", ")
EndFor
(PARI) a(n)=([0, 1, 0, 0, 0, 0, 0; 0, 0, 1, 0, 0, 0, 0; 0, 0, 0, 1, 0, 0, 0; 0, 0, 0, 0, 1, 0, 0; 0, 0, 0, 0, 0, 1, 0; 0, 0, 0, 0, 0, 0, 1; 1, 1, 0, 2, 2, 0, 1]^(n2)*[0; 2; 3; 4; 10; 12; 14])[1, 1] \\ Charles R Greathouse IV, Jun 16 2015


CROSSREFS

Cf. A074148 (Heart patterns), A229093 (Clubs patterns  fixed orientation), A229154 (Clubs Patterns  rotation allowed)


KEYWORD

nonn,easy


AUTHOR



EXTENSIONS



STATUS

approved



