$ time echo '2^500000-1'|bc >/dev/null 
real    0m3.057s
user    0m2.920s
sys     0m0.010s

$ time perl -e 'use bigint only => 'GMP'; my $x = 2 ** 500000 - 1; print $x' >/dev/null 
real    0m0.201s
user    0m0.160s
sys     0m0.010s