>>269よりも原始的（直感的）に

> n <- 1:50; 2^n - n^2
[1] 1.000000e+00 0.000000e+00 -1.000000e+00 0.000000e+00 7.000000e+00
[6] 2.800000e+01 7.900000e+01 1.920000e+02 4.310000e+02 9.240000e+02
[11] 1.927000e+03 3.952000e+03 8.023000e+03 1.618800e+04 3.254300e+04
[16] 6.528000e+04 1.307830e+05 2.618200e+05 5.239270e+05 1.048176e+06
[21] 2.096711e+06 4.193820e+06 8.388079e+06 1.677664e+07 3.355381e+07
[26] 6.710819e+07 1.342170e+08 2.684347e+08 5.368701e+08 1.073741e+09
[31] 2.147483e+09 4.294966e+09 8.589934e+09 1.717987e+10 3.435974e+10
[36] 6.871948e+10 1.374390e+11 2.748779e+11 5.497558e+11 1.099512e+12
[41] 2.199023e+12 4.398047e+12 8.796093e+12 1.759219e+13 3.518437e+13
[46] 7.036874e+13 1.407375e+14 2.814750e+14 5.629500e+14 1.125900e+15

2個しかないんだな。