21002120257 has 2 divisors, whose sum is σ = 21002120258.
Its totient is φ = 21002120256.
The previous prime is 21002120213. The next prime is 21002120261. The reversal of 21002120257 is 75202120012.
Adding to 21002120257 its reverse (75202120012), we get a palindrome (96204240269).
It is a strong prime.
It can be written as a sum of positive squares in only one way, i.e., 14047227441 + 6954892816 = 118521^2 + 83396^2
It is a cyclic number.
It is not a de Polignac number, because 21002120257 - 27 = 21002120129 is a prime.
It is a super-4 number, since 4×210021202574 (a number of 42 digits) contains 4444 as substring.
It is not a weakly prime, because it can be changed into another prime (21002120287) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (17) of ones.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501060128 + 10501060129.
It is an arithmetic number, because the mean of its divisors is an integer number (10501060129).
Almost surely, 221002120257 is an apocalyptic number.
It is an amenable number.
21002120257 is a deficient number, since it is larger than the sum of its proper divisors (1).
21002120257 is an equidigital number, since it uses as much as digits as its factorization.
21002120257 is an odious number, because the sum of its binary digits is odd.
The product of its (nonzero) digits is 560, while the sum is 22.
The spelling of 21002120257 in words is "twenty-one billion, two million, one hundred twenty thousand, two hundred fifty-seven".