21220661 has 8 divisors (see below), whose sum is σ = 26457024. Its totient is φ = 16535520.

The previous prime is 21220649. The next prime is 21220687. The reversal of 21220661 is 16602212.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21220661 - 2⁶ = 21220597 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21220601) 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 7 ways as a sum of consecutive naturals, for example, 137720 + ... + 137873.

It is an arithmetic number, because the mean of its divisors is an integer number (3307128).

Almost surely, 2^21220661 is an apocalyptic number.

It is an amenable number.

21220661 is a deficient number, since it is larger than the sum of its proper divisors (5236363).

21220661 is a wasteful number, since it uses less digits than its factorization.

21220661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 275611.

The product of its (nonzero) digits is 288, while the sum is 20.

The square root of 21220661 is about 4606.5888681323. The cubic root of 21220661 is about 276.8553811596.

Adding to 21220661 its reverse (16602212), we get a palindrome (37822873).

The spelling of 21220661 in words is "twenty-one million, two hundred twenty thousand, six hundred sixty-one".