The answer is "Magic Year" or "Magic Birthday". During that year, things are supposed to go especially well for you.
There are 900 of them.
In Real numbers, each is the additive inverse of the other.
They are called twins.
Because exponent is the same as power.
This is called the "commutative" property.
If you mean can be read the same back to front as front to back such as 12321 or 75257 its a palindrome.
Equivalent numbers.
Palindromes
Two atoms with the same number of protons but different numbers of neutrons are called "isotopes".
Opposite numbers.
They are called isotopes.
There are 900 of them.
300
These atoms are called isotopes.
Five babies born at the same time are called 'quintuplets'. They are also called 'rare'.
If you mean "What are eight babies born on the same day called?": Octuplets (if born by the same mother)
In Real numbers, each is the additive inverse of the other.