func exp10(n int) *big.Int {
	if n < len(nat) {
		return nat[n]
	}
	r := big.NewInt(int64(n))
	return r.Exp(natTen, r, nil)
}
func exp10(n int) *big.Int {
	if n < len(nat) {
		return nat[n]
	}
	r := big.NewInt(int64(n))
	return r.Exp(natTen, r, nil)
}
func exp10 ( n int ) * big . Int { if n < len ( nat ) { return nat [ n ] } r := big . NewInt ( int64 ( n ) ) return r . Exp ( natTen , r , nil ) }
// performance: tested with reference work variable
// - but int.Set is expensive, so let's live with big.Int creation for n >= len(nat)
performance : tested with reference work variable - but int . Set is expensive so let s live with big . Int creation for n > = len ( nat )