21018591 has 24 divisors (see below), whose sum is σ = 34266960. Its totient is φ = 12297600.

The previous prime is 21018563. The next prime is 21018601. The reversal of 21018591 is 19581012.

It is not a de Polignac number, because 21018591 - 2⁹ = 21018079 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21018551) 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, 790 + ... + 6531.

It is an arithmetic number, because the mean of its divisors is an integer number (1427790).

Almost surely, 2^21018591 is an apocalyptic number.

21018591 is a deficient number, since it is larger than the sum of its proper divisors (13248369).

21018591 is a wasteful number, since it uses less digits than its factorization.

21018591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7367 (or 7364 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 27.

The square root of 21018591 is about 4584.6036906149. The cubic root of 21018591 is about 275.9738081636.

It can be divided in two parts, 210185 and 91, that added together give a triangular number (210276 = T₆₄₈).

The spelling of 21018591 in words is "twenty-one million, eighteen thousand, five hundred ninety-one".