|
|
A093820
|
|
a(n) = Sum_{k=1..n-1} gcd(n, a(k)) for n > 1; a(1) = 1.
|
|
3
|
|
|
1, 1, 2, 4, 4, 8, 6, 22, 10, 24, 20, 42, 12, 36, 32, 64, 16, 64, 18, 82, 50, 60, 22, 144, 60, 48, 64, 96, 28, 172, 30, 282, 78, 64, 70, 256, 36, 72, 106, 254, 80, 204, 84, 176, 166, 88, 92, 518, 78, 200, 136, 210, 104, 244, 134, 346, 96, 112, 58, 538, 120, 120, 216
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,3
|
|
COMMENTS
|
a(n) = n-1 iff n is prime.
a(n) >= n-1. All terms except a(1) = a(2) = 1 are even. - Ivan Neretin, Apr 06 2016
|
|
LINKS
|
|
|
MATHEMATICA
|
Fold[Append[#1, Total@GCD[#1, #2]] &, {1}, Range[2, 64]] (* Ivan Neretin, Apr 06 2016 *)
|
|
PROG
|
(PARI) lista(nn) = {va = vector(nn); va[1] = 1; for (i = 2, nn, va[i] = sum(k=1, i-1, gcd(i, va[k])); ); va; } \\ Michel Marcus, Oct 04 2013
(Haskell)
a093820 n = a093820_list !! (n-1)
a093820_list = 1 : f [2..] [1] where
f (x:xs) ys = y : f xs (y:ys) where y = sum $ map (gcd x) ys
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|