OFFSET
1,1
COMMENTS
This is a subset of A003418 such that lcm(1,2,...,n-1) <> lcm(1,2,...,n) <> lcm(1,2,...,n+1) for (n>=1).
lcm(1,2,...,n) will be unique if both n and n+1 can be expressed as different prime powers, i.e., n = p^a and n+1 = q^b where p,q are prime and a,b are integers.
FORMULA
EXAMPLE
lcm(1,2,...,7) is 420 and lcm(1,2,...,7,2^3) is 840 so 420 and 840 are in the sequence.
But lcm(1,2,...,7,2^3,3^2) = lcm(1,2...,7,2^3,3^2,(2*5)) = 2520. If n=9, n+1 is not a prime power and 2520 is not unique. So 2520 is not in the sequence.
CROSSREFS
KEYWORD
nonn
AUTHOR
Adrian Pietkiewicz, Jan 18 2018
STATUS
approved