21536991 has 24 divisors (see below), whose sum is σ = 35909120. Its totient is φ = 12183696.

The previous prime is 21536989. The next prime is 21537001. The reversal of 21536991 is 19963512.

It is not a de Polignac number, because 21536991 - 2¹ = 21536989 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21536191) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4830 + ... + 8148.

Almost surely, 2^21536991 is an apocalyptic number.

21536991 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21536991 is a deficient number, since it is larger than the sum of its proper divisors (14372129).

21536991 is a wasteful number, since it uses less digits than its factorization.

21536991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3435 (or 3432 counting only the distinct ones).

The product of its digits is 14580, while the sum is 36.

The square root of 21536991 is about 4640.7963756235. The cubic root of 21536991 is about 278.2242682472.

The spelling of 21536991 in words is "twenty-one million, five hundred thirty-six thousand, nine hundred ninety-one".