>>670
PowerShell

function f([BigInt]$n)
{
　　$c = [char[]][string]$n
　　$n - [BigInt]-join $c[-1..-$c.length]
}

12345, [BigInt]::Pow(12, 34) |% {"$_ → $(f $_)"}

[実行結果]
12345 → -41976
4922235242952026704037113243122008064 → 314233029528909439273950854852378624