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A039721 a(1) = 1, a(m+1) = 2*Sum_{k=1..floor((m+1)/2)} a(m+1-k). 2
1, 2, 4, 12, 32, 96, 280, 840, 2496, 7488, 22400, 67200, 201408, 604224, 1812112, 5436336, 16307328, 48921984, 146760960, 440282880, 1320833664, 3962500992, 11887458176, 35662374528, 106986989184, 320960967552, 962882499840, 2888647499520, 8665941290112 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
FORMULA
a(1)=1, a(2)=2, a(2m+1)=3*a(2m)-2*a(m), a(2m+2)=3*a(2m+1) (m is positive integer).
EXAMPLE
a(6)=2*(a(5)+a(4)+a(3)) = 2*(32+12+4) = 96.
MAPLE
a[1]:= 1;
for m from 1 to 100 do
a[m+1]:= 2*add(a[m+1-k], k=1..floor((m+1)/2));
od:
seq(a[i], i=1..100); # Robert Israel, May 18 2014
MATHEMATICA
Fold[Append[#1, 2 Total[#1[[#2 - Range[Floor[#2/2] ] ]] ] ] &, {1}, Range[2, 29]] (* Michael De Vlieger, Dec 11 2017 *)
PROG
(PARI) lista(nn) = {v = vector(nn); v[1] = 1; for (n=2, nn, v[n] = 2*sum(k=1, n\2, v[n-k]); ); v; } \\ Michel Marcus, May 18 2014
CROSSREFS
Cf. A039722 (similar definition).
Sequence in context: A231295 A087211 A161177 * A148193 A341344 A002528
KEYWORD
easy,nonn
AUTHOR
Leroy Quet, Dec 11 1999
EXTENSIONS
More terms from James A. Sellers, May 04 2000
Two more terms from Michel Marcus, May 18 2014
STATUS
approved

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Last modified June 17 03:50 EDT 2024. Contains 373432 sequences. (Running on oeis4.)