21650991 has 4 divisors (see below), whose sum is σ = 28867992. Its totient is φ = 14433992.

The previous prime is 21650971. The next prime is 21650999. The reversal of 21650991 is 19905612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21650991 - 2¹⁰ = 21649967 is a prime.

It is a super-2 number, since 2×21650991² = 937530822564162, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21650999) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3608496 + ... + 3608501.

It is an arithmetic number, because the mean of its divisors is an integer number (7216998).

Almost surely, 2^21650991 is an apocalyptic number.

21650991 is a deficient number, since it is larger than the sum of its proper divisors (7217001).

21650991 is an equidigital number, since it uses as much as digits as its factorization.

21650991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7217000.

The product of its (nonzero) digits is 4860, while the sum is 33.

The square root of 21650991 is about 4653.0625398763. The cubic root of 21650991 is about 278.7143052553.

The spelling of 21650991 in words is "twenty-one million, six hundred fifty thousand, nine hundred ninety-one".