21166491 has 16 divisors (see below), whose sum is σ = 29352960. Its totient is φ = 13550880.

The previous prime is 21166489. The next prime is 21166499. The reversal of 21166491 is 19466112.

It is a happy number.

It is not a de Polignac number, because 21166491 - 2¹ = 21166489 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21166499) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 18856 + ... + 19946.

It is an arithmetic number, because the mean of its divisors is an integer number (1834560).

Almost surely, 2^21166491 is an apocalyptic number.

21166491 is a deficient number, since it is larger than the sum of its proper divisors (8186469).

21166491 is a wasteful number, since it uses less digits than its factorization.

21166491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1346.

The product of its digits is 2592, while the sum is 30.

The square root of 21166491 is about 4600.7054893788. The cubic root of 21166491 is about 276.6196040979.

The spelling of 21166491 in words is "twenty-one million, one hundred sixty-six thousand, four hundred ninety-one".