21661021 has 8 divisors (see below), whose sum is σ = 22353120. Its totient is φ = 20974608.

The previous prime is 21661001. The next prime is 21661027. The reversal of 21661021 is 12016612.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21661021 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21661021.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661027) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7110 + ... + 9688.

It is an arithmetic number, because the mean of its divisors is an integer number (2794140).

Almost surely, 2^21661021 is an apocalyptic number.

It is an amenable number.

21661021 is a deficient number, since it is larger than the sum of its proper divisors (692099).

21661021 is a wasteful number, since it uses less digits than its factorization.

21661021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2843.

The product of its (nonzero) digits is 144, while the sum is 19.

The square root of 21661021 is about 4654.1401998651. The cubic root of 21661021 is about 278.7573375105.

Adding to 21661021 its reverse (12016612), we get a palindrome (33677633).

The spelling of 21661021 in words is "twenty-one million, six hundred sixty-one thousand, twenty-one".