21009671 has 16 divisors (see below), whose sum is σ = 23351328. Its totient is φ = 18816000.

The previous prime is 21009643. The next prime is 21009679. The reversal of 21009671 is 17690012.

It is a cyclic number.

It is not a de Polignac number, because 21009671 - 2²² = 16815367 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 21009671.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21009679) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 29621 + ... + 30321.

It is an arithmetic number, because the mean of its divisors is an integer number (1459458).

Almost surely, 2^21009671 is an apocalyptic number.

21009671 is a deficient number, since it is larger than the sum of its proper divisors (2341657).

21009671 is a wasteful number, since it uses less digits than its factorization.

21009671 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 802.

The product of its (nonzero) digits is 756, while the sum is 26.

The square root of 21009671 is about 4583.6307661067. The cubic root of 21009671 is about 275.9347628142.

Adding to 21009671 its reverse (17690012), we get a palindrome (38699683).

The spelling of 21009671 in words is "twenty-one million, nine thousand, six hundred seventy-one".