21781128 has 32 divisors (see below), whose sum is σ = 54590400. Its totient is φ = 7242048.

The previous prime is 21781093. The next prime is 21781129. The reversal of 21781128 is 82118712.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 21781095 and 21781104.

It is not an unprimeable number, because it can be changed into a prime (21781129) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11325 + ... + 13107.

It is an arithmetic number, because the mean of its divisors is an integer number (1705950).

Almost surely, 2^21781128 is an apocalyptic number.

It is an amenable number.

21781128 is an abundant number, since it is smaller than the sum of its proper divisors (32809272).

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

21781128 is a wasteful number, since it uses less digits than its factorization.

21781128 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2301 (or 2297 counting only the distinct ones).

The product of its digits is 1792, while the sum is 30.

The square root of 21781128 is about 4667.0256052437. The cubic root of 21781128 is about 279.2716102170.

The spelling of 21781128 in words is "twenty-one million, seven hundred eighty-one thousand, one hundred twenty-eight".