A100675 - OEIS

A100675

a(1) = 1; for n >= 1, a(n+1) = Sum_{k=1..n} gcd(k, a(n)).

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

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OFFSET

1,3

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

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

Adjacent sequences: A100672 A100673 A100674 * A100676 A100677 A100678

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