

A151906


a(0) = 0, a(1) = 1; for n>1, a(n) = 8*A151905(n) + 4.


7



0, 1, 4, 4, 4, 12, 4, 4, 12, 12, 12, 36, 4, 4, 12, 12, 12, 36, 12, 12, 36, 36, 36, 108, 4, 4, 12, 12, 12, 36, 12, 12, 36, 36, 36, 108, 12, 12, 36, 36, 36, 108, 36, 36, 108, 108, 108, 324, 4, 4, 12, 12, 12, 36, 12, 12, 36, 36, 36, 108, 12, 12, 36, 36, 36, 108, 36, 36, 108, 108, 108
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OFFSET

0,3


COMMENTS

Consider the HolladayUlam CA shown in Fig. 2 and Example 2 of the Ulam article. Then a(n) is the number of cells turned ON in generation n.


REFERENCES

S. Ulam, On some mathematical problems connected with patterns of growth of figures, pp. 215224 of R. E. Bellman, ed., Mathematical Problems in the Biological Sciences, Proc. Sympos. Applied Math., Vol. 14, Amer. Math. Soc., 1962.


LINKS

Table of n, a(n) for n=0..70.
David Applegate, The movie version
David Applegate, Omar E. Pol and N. J. A. Sloane, The Toothpick Sequence and Other Sequences from Cellular Automata
N. J. A. Sloane, Catalog of Toothpick and Cellular Automata Sequences in the OEIS
N. J. A. Sloane, Illustration of initial terms (annotated copy of figure on p. 222 of Ulam)


FORMULA

The three trisections are essentially A147582, A147582 and 3*A147582 respectively. More precisely, For t >= 1, a(3t) = a(3t+1) = A147582(t+1) = 4*3^(wt(t)1), a(3t+2) = 4*A147582(t+1) = 4*3^wt(t). See A151907 for explanation.


EXAMPLE

From Omar E. Pol, Apr 02 2018: (Start)
Note that this sequence also can be written as an irregular triangle read by rows in which the row lengths are the terms of A011782 multiplied by 3, as shown below:
0,1, 4;
4,4,12;
4,4,12,12,12,36;
4,4,12,12,12,36,12,12,36,36,36,108;
4,4,12,12,12,36,12,12,36,36,36,108,12,12,36,36,36,108,36,36,108,108,108,324;
4,4,12,12,12,36,12,12,36,36,36,108,12,12,36,36,36,108,36,36,108,108,108,... (End)


MAPLE

f := proc(n) local j; j:=n mod 6; if (j<=1) then 0 elif (j<=4) then 1 else 2; fi; end;
wt := proc(n) local w, m, i; w := 0; m := n; while m > 0 do i := m mod 2; w := w+i; m := (mi)/2; od; w; end;
A151904 := proc(n) local k, j; k:=floor(n/6); j:=n6*k; (3^(wt(k)+f(j))1)/2; end;
A151905 := proc (n) local k, j;
if (n=0) then 0;
elif (n=1) then 1;
elif (n=2) then 0;
else k:=floor( log(n/3)/log(2) ); j:=n3*2^k; A151904(j); fi;
end;
A151906 := proc(n);
if (n=0) then 0;
elif (n=1) then 1;
else 8*A151905(n) + 4;
fi;
end;


CROSSREFS

Cf. A151904, A151905, A151907, A139250, A151895, A151896.
Sequence in context: A220931 A219578 A219373 * A151896 A267191 A170897
Adjacent sequences: A151903 A151904 A151905 * A151907 A151908 A151909


KEYWORD

nonn,tabf


AUTHOR

David Applegate and N. J. A. Sloane, Jul 31 2009, Aug 03 2009


STATUS

approved



