21000120257 has 2 divisors, whose sum is σ = 21000120258. Its totient is φ = 21000120256.

The previous prime is 21000120221. The next prime is 21000120269. The reversal of 21000120257 is 75202100012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10668617521 + 10331502736 = 103289^2 + 101644^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000120257 - 2¹⁰ = 21000119233 is a prime.

It is not a weakly prime, because it can be changed into another prime (21000120217) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500060128 + 10500060129.

It is an arithmetic number, because the mean of its divisors is an integer number (10500060129).

Almost surely, 2^21000120257 is an apocalyptic number.

It is an amenable number.

21000120257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21000120257 is an equidigital number, since it uses as much as digits as its factorization.

21000120257 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 280, while the sum is 20.

Adding to 21000120257 its reverse (75202100012), we get a palindrome (96202220269).

The spelling of 21000120257 in words is "twenty-one billion, one hundred twenty thousand, two hundred fifty-seven".