21956661 has 12 divisors (see below), whose sum is σ = 32390592. Its totient is φ = 14326056.

The previous prime is 21956621. The next prime is 21956687. The reversal of 21956661 is 16665912.

It is not a de Polignac number, because 21956661 - 2¹¹ = 21954613 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 (21956611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 25531 + ... + 26376.

It is an arithmetic number, because the mean of its divisors is an integer number (2699216).

Almost surely, 2^21956661 is an apocalyptic number.

It is an amenable number.

21956661 is a deficient number, since it is larger than the sum of its proper divisors (10433931).

21956661 is a wasteful number, since it uses less digits than its factorization.

21956661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51960 (or 51957 counting only the distinct ones).

The product of its digits is 19440, while the sum is 36.

The square root of 21956661 is about 4685.7935293822. The cubic root of 21956661 is about 280.0198157745.

The spelling of 21956661 in words is "twenty-one million, nine hundred fifty-six thousand, six hundred sixty-one".