Solving Project Euler problem #48 in Scala
Your solution is clean but doesn't scale well. A well known optimization for a^k mod m is to perform all computations modulus m. If m is sufficiently small, we furthermore can switch to native types (this is not the case here !).

val n = 1000
val m = BigInt(10).pow(10)
(for (i &lt;- 1 to n) yield BigInt(i).modPow(i,m)).sum % m


Rounded avarage timing results (Scala 2.9.1 with -optimize) :

n                     1000     | 10000
Initial solution       4.8 ms  |  6700 ms
Fold left              4.8 ms  |  6700 ms
My humble version      0.5 ms  |     5 ms