21981231 has 6 divisors (see below), whose sum is σ = 31750680. Its totient is φ = 14654148.

The previous prime is 21981229. The next prime is 21981251. The reversal of 21981231 is 13218912.

It is not a de Polignac number, because 21981231 - 2¹ = 21981229 is a prime.

It is a super-2 number, since 2×21981231² = 966349032550722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21981195 and 21981204.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21981251) 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, 1221171 + ... + 1221188.

It is an arithmetic number, because the mean of its divisors is an integer number (5291780).

Almost surely, 2^21981231 is an apocalyptic number.

21981231 is a deficient number, since it is larger than the sum of its proper divisors (9769449).

21981231 is a wasteful number, since it uses less digits than its factorization.

21981231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2442365 (or 2442362 counting only the distinct ones).

The product of its digits is 864, while the sum is 27.

The square root of 21981231 is about 4688.4145507837. The cubic root of 21981231 is about 280.1242263395.

The spelling of 21981231 in words is "twenty-one million, nine hundred eighty-one thousand, two hundred thirty-one".