21006256621 has 8 divisors (see below), whose sum is σ = 24008565440. Its totient is φ = 18004301568.

The previous prime is 21006256619. The next prime is 21006256681. The reversal of 21006256621 is 12665260012.

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 21006256621 - 2¹ = 21006256619 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 (21006256681) 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, 54130 + ... + 211996.

It is an arithmetic number, because the mean of its divisors is an integer number (3001070680).

Almost surely, 2^21006256621 is an apocalyptic number.

It is an amenable number.

21006256621 is a deficient number, since it is larger than the sum of its proper divisors (3002308819).

21006256621 is a wasteful number, since it uses less digits than its factorization.

21006256621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 176883.

The product of its (nonzero) digits is 8640, while the sum is 31.

The spelling of 21006256621 in words is "twenty-one billion, six million, two hundred fifty-six thousand, six hundred twenty-one".