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