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A100675
a(1) = 1; for n >= 1, a(n+1) = Sum_{k=1..n} gcd(k, a(n)).
2
1, 1, 2, 4, 8, 9, 10, 14, 18, 27, 22, 26, 18, 37, 14, 40, 56, 59, 18, 64, 56, 73, 22, 64, 68, 65, 70, 92, 78, 105, 126, 148, 64, 113, 34, 100, 140, 199, 38, 112, 170, 157, 42, 196, 154, 181, 46, 136, 168, 309, 82, 116, 132, 271, 54, 244, 112, 285, 254, 88, 238, 227, 62
OFFSET
1,3
LINKS
MAPLE
a[1]:=1: for n from 2 to 80 do b[n]:=[seq(gcd(k, a[n-1]), k=1..n-1)]: a[n]:=sum(b[n][j], j=1..nops(b[n])) od: seq(a[n], n=1..80);
MATHEMATICA
a[1] = 1; a[n_] := a[n] = Plus @@ GCD[Table[i, {i, n - 1}], a[n - 1]]; Table[ a[n], {n, 62}] (* Robert G. Wilson v, Dec 09 2004 *)
nxt[{n_, a_}]:={n+1, Total[GCD[Range[n], a]]}; NestList[nxt, {1, 1}, 70][[All, 2]] (* Harvey P. Dale, Sep 10 2019 *)
CROSSREFS
Sequence in context: A326713 A328945 A050907 * A196730 A325942 A325944
KEYWORD
nonn
AUTHOR
Leroy Quet, Dec 06 2004
EXTENSIONS
More terms from Emeric Deutsch and Robert G. Wilson v, Dec 09 2004
Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, Jun 16 2007
STATUS
approved