21020420256 has 48 divisors (see below), whose sum is σ = 60194842848. Its totient is φ = 6369824000.

The previous prime is 21020420249. The next prime is 21020420261. The reversal of 21020420256 is 65202402012.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (48).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9951795 + ... + 9953906.

It is an arithmetic number, because the mean of its divisors is an integer number (1254059226).

Almost surely, 2^21020420256 is an apocalyptic number.

It is an amenable number.

21020420256 is an abundant number, since it is smaller than the sum of its proper divisors (39174422592).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21020420256 is a wasteful number, since it uses less digits than its factorization.

21020420256 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19905725 (or 19905717 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 24.

Adding to 21020420256 its reverse (65202402012), we get a palindrome (86222822268).

The spelling of 21020420256 in words is "twenty-one billion, twenty million, four hundred twenty thousand, two hundred fifty-six".