21780028 has 6 divisors (see below), whose sum is σ = 38115056. Its totient is φ = 10890012.

The previous prime is 21780007. The next prime is 21780037. The reversal of 21780028 is 82008712.

It is a junction number, because it is equal to n+sod(n) for n = 21779978 and 21780005.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2722500 + ... + 2722507.

Almost surely, 2^21780028 is an apocalyptic number.

It is an amenable number.

21780028 is a deficient number, since it is larger than the sum of its proper divisors (16335028).

21780028 is a wasteful number, since it uses less digits than its factorization.

21780028 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5445011 (or 5445009 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 28.

The square root of 21780028 is about 4666.9077556772. The cubic root of 21780028 is about 279.2669088391.

The spelling of 21780028 in words is "twenty-one million, seven hundred eighty thousand, twenty-eight".