21287621 has 8 divisors (see below), whose sum is σ = 22581504. Its totient is φ = 19998400.

The previous prime is 21287551. The next prime is 21287633. The reversal of 21287621 is 12678212.

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-21287621 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21287641) 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 7 ways as a sum of consecutive naturals, for example, 13946 + ... + 15396.

It is an arithmetic number, because the mean of its divisors is an integer number (2822688).

Almost surely, 2^21287621 is an apocalyptic number.

It is an amenable number.

21287621 is a deficient number, since it is larger than the sum of its proper divisors (1293883).

21287621 is a wasteful number, since it uses less digits than its factorization.

21287621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2331.

The product of its digits is 2688, while the sum is 29.

The square root of 21287621 is about 4613.8509945598. The cubic root of 21287621 is about 277.1462733208.

The spelling of 21287621 in words is "twenty-one million, two hundred eighty-seven thousand, six hundred twenty-one".