| crypto/rand | Package rand implements a cryptographically secure random number generator. |
| fmt | Package fmt implements formatted I/O with functions analogous to C's printf and scanf. |
| math | Package math provides basic constants and mathematical functions. |
| math/big | Package big implements arbitrary-precision arithmetic (big numbers). |
| math/rand | Package rand implements pseudo-random number generators suitable for tasks such as simulation, but it should not be used for security-sensitive work. |
| sync | Package sync provides basic synchronization primitives such as mutual exclusion locks. |
| time | Package time provides functionality for measuring and displaying time. |