OFFSET

1,2

EXAMPLE

a(1) = 1 (which is the only number with exactly 1 divisor).

a(2) = 5 (since 5 is the smallest prime that is 5-rough).

a(3) = 25 (since 5 is the smallest number that is the square of a 5-rough prime).

a(4) = 35 (since a number with 4 divisors must be either the cube of a prime or the product of two distinct primes, and the smallest 5-rough numbers of these two types are 5^3 = 125 and 5*7 = 35, respectively, and 35 is the smaller of the two).

CROSSREFS

KEYWORD

nonn

AUTHOR

Jon E. Schoenfield, Mar 18 2023

STATUS

approved