Testing for signature: [14.0, 18.0, 5.0, 11.0, 13.0, 2.0, 12.0, 2.0, 13.0, 0.0, 2.0, 9.0, 10.0, 19.0, 1.0, 13.0, 3.0, 16.0, 3.0] and n: 67
14.0 18.0 5.0 11.0 13.0 2.0 12.0 2.0 13.0 0.0 2.0 9.0 10.0 19.0 1.0 13.0 3.0 16.0 3.0 166.0 318.0 618.0 1231.0 2451.0 4889.0 9776.0 19540.0 39078.0 78143.0 156286.0 312570.0 625131.0 1250252.0 2500485.0 5000969.0 1.0001925E7 2.0003847E7 4.0007678E7 8.0015353E7 1.6003054E8 3.20060762E8 6.40120906E8 1.280240581E9 2.560478711E9 5.120952533E9 1.024189529E10 2.048377104E10 4.0967503002E10 8.1934927861E10 1.63869699436E11 3.27739086302E11 6.55477547473E11 1.310953844694E12 2.621905188903E12 5.243805376837E12 1.0487600751749E13 2.0975181499651E13 4.1950322991624E13 8.3900565967895E13 1.6780097190525E14 3.35601623749738E14 6.7120260737857E14 1.342403934516559E15 2.684805308554407E15 5.369605496156281E15 1.0739200750417272E16 2.1478381017063504E16 expected:<1.0739200750417274E16> but was:<1.0739200750417272E16>

i think int n is too large that it will be wrong when implement sum x previous

i like your solution :).
i think break out for when s.contains(String.valueOf(i)) = true.