21091231 has 8 divisors (see below), whose sum is σ = 24149664. Its totient is φ = 18044160.

The previous prime is 21091201. The next prime is 21091249. The reversal of 21091231 is 13219012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21091231 - 2¹³ = 21083039 is a prime.

It is a super-2 number, since 2×21091231² = 889680050190722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21091199 and 21091208.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21091201) 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, 1611 + ... + 6691.

It is an arithmetic number, because the mean of its divisors is an integer number (3018708).

Almost surely, 2^21091231 is an apocalyptic number.

21091231 is a deficient number, since it is larger than the sum of its proper divisors (3058433).

21091231 is an equidigital number, since it uses as much as digits as its factorization.

21091231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5681.

The product of its (nonzero) digits is 108, while the sum is 19.

The square root of 21091231 is about 4592.5190255458. The cubic root of 21091231 is about 276.2913633524.

The spelling of 21091231 in words is "twenty-one million, ninety-one thousand, two hundred thirty-one".