OFFSET
1,1
FORMULA
a(n) = A289280(a(n-1)) - 1 for n > 1.
EXAMPLE
a(2) = 3 since 4 is the smallest k > a(1) such that rad(k) | a(1), and 4 - 1 = 3.
a(3) = 8 since 9 is the least k > a(2) such that rad(k) | a(2), and 9 - 1 = 8.
a(4) = 15 since 16 is the least k > a(3) such that rad(k) | a(3), and 16 - 1 = 15, etc.
MATHEMATICA
rad[x_] := rad[x] = Times @@ FactorInteger[x][[All, 1]];
NestList[(k = # + 1; While[! Divisible[#, rad[k]], k++]; k - 1) &, 2, 20]
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Michael De Vlieger, Nov 15 2023
STATUS
approved