21025881 has 6 divisors (see below), whose sum is σ = 30370730. Its totient is φ = 14017248.

The previous prime is 21025867. The next prime is 21025883. The reversal of 21025881 is 18852012.

It can be written as a sum of positive squares in only one way, i.e., 18352656 + 2673225 = 4284^2 + 1635^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21025881 is a prime.

It is a super-2 number, since 2×21025881² = 884175343652322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21025883) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1168096 + ... + 1168113.

Almost surely, 2^21025881 is an apocalyptic number.

It is an amenable number.

21025881 is a deficient number, since it is larger than the sum of its proper divisors (9344849).

21025881 is a wasteful number, since it uses less digits than its factorization.

21025881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2336215 (or 2336212 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 27.

The square root of 21025881 is about 4585.3986740522. The cubic root of 21025881 is about 276.0057103418.

Adding to 21025881 its reverse (18852012), we get a palindrome (39877893).

The spelling of 21025881 in words is "twenty-one million, twenty-five thousand, eight hundred eighty-one".