Make lcm() symbolic

[ppurka]

From google spreadsheet which no one reads X-(

sage: sum(lcm(10,x), x, 1, 10)  # Incorrect
550

sage: sum([lcm(10,i) for i in xrange(1,11)])  # Correct
320

CC: @kcrisman @sagetrac-kbaut @sagetrac-jakobkroeker

Component: symbolics

Stopgaps: todo

Issue created by migration from https://trac.sagemath.org/ticket/15497

[kcrisman]

comment:2

Here is the problem, presumably (lcm not being symbolic in this way):

sage: lcm(10,x)
10*x

We can all be Gauss with this.

sage: sum(lcm(1,x),x,1,100)
5050

The solution is to make sure that lcm(a,b) does something symbolic, or throws an error, when we feed it symbolic entries. Is there already a ticket for this, perhaps?

[kcrisman]

comment:8

See also #16721.