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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 Robert Israel, Table of n, a(n) for n = 1..212 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 A002528 A216818 Adjacent sequences:  A039718 A039719 A039720 * A039722 A039723 A039724 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 October 21 22:47 EDT 2019. Contains 328315 sequences. (Running on oeis4.)