Pattern matching in vim

I have a file with following content:

635147+876+5597+1686+54=8643360
2415+382376+88324+81544+926+68619475+677+222852=69398589
80+21+4478882+8945092=13424075
62+9598=9660
16832904+537+51460155+6822+2+4901436+47443+5669+855928+8113549+424282=82648727
33+9872=9905
555839
5017598+5639262+4+62+9413+4+4991+41568=10712902
4977+164+77+1018643+593851+83730=1701442
220+6831+26=7077
5+54102+1034451=1088558
37844
1
35+2983325+0+6400=2989760
8081+8361365+6+477=8369929
66+68232+9406935+6489662=15964895
6569+59336692+75+11328=59354664
28332+725+2683+45913425+9648987+4911=55599063
69724687+8+7+9940+5568+29585+518916=70288711
1804642
659157+5144361+7072+16+4799+811+58742059+451875+138174=65148324
2288508+509472+43+83704=2881727
872027+1115415+1+47922+547008+56+5550+71642773+948394=75179146
142

I would like to sort it to this:

16832904+537+51460155+6822+2+4901436+47443+5669+855928+8113549+424282=82648727
872027+1115415+1+47922+547008+56+5550+71642773+948394=75179146
69724687+8+7+9940+5568+29585+518916=70288711
2415+382376+88324+81544+926+68619475+677+222852=69398589
659157+5144361+7072+16+4799+811+58742059+451875+138174=65148324
6569+59336692+75+11328=59354664
28332+725+2683+45913425+9648987+4911=55599063
66+68232+9406935+6489662=15964895
80+21+4478882+8945092=13424075
5017598+5639262+4+62+9413+4+4991+41568=10712902
635147+876+5597+1686+54=8643360
8081+8361365+6+477=8369929
35+2983325+0+6400=2989760
2288508+509472+43+83704=2881727
1804642
4977+164+77+1018643+593851+83730=1701442
5+54102+1034451=1088558
555839
37844
33+9872=9905
62+9598=9660
220+6831+26=7077
142
1

I'm able to do this with with for example :sor! n /\(^[0-9]*$\|=.*\)/ r. However, for some reason, :sor! n /\(^[0-9]+$\|=.*\)/ r does not work. Why is that so? + should mean one or more numbers in my example?