21533661 has 32 divisors (see below), whose sum is σ = 33177600. Its totient is φ = 13794480.

The previous prime is 21533647. The next prime is 21533683. The reversal of 21533661 is 16633512.

It is not a de Polignac number, because 21533661 - 2⁶ = 21533597 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

Its product of digits (3240) is a multiple of the sum of its prime divisors (360).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21533861) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 89980 + ... + 90218.

It is an arithmetic number, because the mean of its divisors is an integer number (1036800).

Almost surely, 2^21533661 is an apocalyptic number.

It is an amenable number.

21533661 is a deficient number, since it is larger than the sum of its proper divisors (11643939).

21533661 is a wasteful number, since it uses less digits than its factorization.

21533661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 366 (or 360 counting only the distinct ones).

The product of its digits is 3240, while the sum is 27.

The square root of 21533661 is about 4640.4375871247. The cubic root of 21533661 is about 278.2099280427.

The spelling of 21533661 in words is "twenty-one million, five hundred thirty-three thousand, six hundred sixty-one".