21545991 has 12 divisors (see below), whose sum is σ = 31162560. Its totient is φ = 14345280.

The previous prime is 21545989. The next prime is 21546001. The reversal of 21545991 is 19954512.

21545991 is a `hidden beast` number, since 21 + 545 + 9 + 91 = 666.

It is not a de Polignac number, because 21545991 - 2¹ = 21545989 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21545911) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 11370 + ... + 13128.

It is an arithmetic number, because the mean of its divisors is an integer number (2596880).

Almost surely, 2^21545991 is an apocalyptic number.

21545991 is a deficient number, since it is larger than the sum of its proper divisors (9616569).

21545991 is a wasteful number, since it uses less digits than its factorization.

21545991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3126 (or 3123 counting only the distinct ones).

The product of its digits is 16200, while the sum is 36.

The square root of 21545991 is about 4641.7659355034. The cubic root of 21545991 is about 278.2630181620.

The spelling of 21545991 in words is "twenty-one million, five hundred forty-five thousand, nine hundred ninety-one".