21020420257 has 4 divisors (see below), whose sum is σ = 21533113476. Its totient is φ = 20507727040.

The previous prime is 21020420249. The next prime is 21020420261. The reversal of 21020420257 is 75202402012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 4234885776 + 16785534481 = 65076^2 + 129559^2 .

It is a cyclic number.

It is not a de Polignac number, because 21020420257 - 2³ = 21020420249 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21020420227) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 256346548 + ... + 256346629.

It is an arithmetic number, because the mean of its divisors is an integer number (5383278369).

Almost surely, 2^21020420257 is an apocalyptic number.

It is an amenable number.

21020420257 is a deficient number, since it is larger than the sum of its proper divisors (512693219).

21020420257 is an equidigital number, since it uses as much as digits as its factorization.

21020420257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 512693218.

The product of its (nonzero) digits is 2240, while the sum is 25.

Adding to 21020420257 its reverse (75202402012), we get a palindrome (96222822269).

The spelling of 21020420257 in words is "twenty-one billion, twenty million, four hundred twenty thousand, two hundred fifty-seven".