infinite series sum (Java 8)

import java.util.function.IntToDoubleFunction;
import java.util.stream.IntStream;

public class Main {
    public static void main(String... args) {
        double x = 0.7034648345913732;
        IntToDoubleFunction termRule = n -> n * Math.pow(x, n);
        IntToDoubleFunction m = accuracyPow -> findSum(termRule, Math.pow(0.1, accuracyPow));
        double sum = m.applyAsDouble(3);
        System.out.println(Math.round(sum));
    }

    static double findSum(IntToDoubleFunction termRule, double precision) {
        int lastInt = numOfRelevantTerms(termRule, precision);
        return IntStream.range(1, lastInt)
                .mapToDouble(termRule)
                .sum();
    }

    static int numOfRelevantTerms(IntToDoubleFunction termRule, double precision) {
        //fibonacci sequence: [1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946, 17711, 28657, 46368, 75025, 121393, 196418, 317811, 514229, 832040, 1346269, 2178309, 3524578, 5702887, 9227465, 14930352, 24157817, 39088169, 63245986, 102334155, 165580141, 267914296, 433494437, 701408733, 1134903170, 1836311903]
        int[] fibo = {13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597};
        for (int i : fibo) {
            double v = termRule.applyAsDouble(i);
            if (v < precision) {
                return i;
            }
        }
        return -1;
    }
}