OFFSET
1,3
LINKS
FORMULA
a(1) = 1; a(n+1) = Sum_{k=1..n} lcm(a(k),a(n))/a(k).
EXAMPLE
a(1) = 1;
a(2) = a(1)/gcd(a(1),a(1)) = 1/gcd(1,1) = 1;
a(3) = a(2)/gcd(a(1),a(2)) + a(2)/gcd(a(2),a(2)) = 1/gcd(1,1) + 1/gcd(1,1) = 2;
a(4) = a(3)/gcd(a(1),a(3)) + a(3)/gcd(a(2),a(3)) + a(3)/gcd(a(3),a(3)) = 2/gcd(1,2) + 2/gcd(1,2) + 2/gcd(2,2) = 5, etc.
MAPLE
A[1]:= 1:
for n from 1 to 50 do
A[n+1]:= add(A[n]/igcd(A[k], A[n]), k=1..n)
od:
seq(A[i], i=1..50); # Robert Israel, Sep 01 2017
MATHEMATICA
a[1] = 1; a[n_] := a[n] = Sum[a[n - 1]/GCD[a[k - 1], a[n - 1]], {k, 2, n}]; Table[a[n], {n, 26}]
a[1] = 1; a[n_] := a[n] = Sum[LCM[a[k - 1], a[n - 1]]/a[k - 1], {k, 2, n}]; Table[a[n], {n, 26}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Aug 31 2017
STATUS
approved