For the l.c.m. of 1,2,...,n Hardy and Wright use U(x)
For reference (or to add more!) the OEIS sequences are
x## : A003418
x# : A003486
pi(x) : A000720
p<=x : A007917
(seqfans: there's a host of analogs for other values of "prime", eg in
quadratic fields)
