# this code demonstrates how to calculate with sed (not highly golfed)
# to ucd (e.g. 125="0-0--0-----")
:0
s/[1-9]/&-/g
y/123456789/012345678/
t0
# to unary number (multiplier only)
h
:1
s/-0/0----------/
t1
s/0//g
x
# make n*2+1
s/-/--/g
s/$/-/
# loop counter
s/$/"/
# mul by n++ twice
:2
y/-/!/
G # load n
:3
s/!\(.*\n\(.*\)\)/\2\1/ # replace each ! with n (unary)
s/0\?-\{10\}/-0/ # carry up if applicable
t3
s/\n.*// # unload n
x
s/$/-/ # n++
x
T
s/"// # counter-- && redo :2
t2
# div by 6
:4
s/------/!/
t4
s/-\(0!*\)/\1!----/
t4
# to decimal
:5
s/!/<12345678901>/
s/\(.\?\)<.*\1\(.\).*>/\2/
t5
# print
Note that non-ascii characters in the above source code will be escaped (such as \x9f).