21106921 has 4 divisors (see below), whose sum is σ = 23025744. Its totient is φ = 19188100.

The previous prime is 21106907. The next prime is 21106933. The reversal of 21106921 is 12960112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21106921 - 2¹⁵ = 21074153 is a prime.

It is a super-2 number, since 2×21106921² = 891004228200482, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21106892 and 21106901.

It is not an unprimeable number, because it can be changed into a prime (21106961) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 959395 + ... + 959416.

It is an arithmetic number, because the mean of its divisors is an integer number (5756436).

Almost surely, 2^21106921 is an apocalyptic number.

It is an amenable number.

21106921 is a deficient number, since it is larger than the sum of its proper divisors (1918823).

21106921 is a wasteful number, since it uses less digits than its factorization.

21106921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1918822.

The product of its (nonzero) digits is 216, while the sum is 22.

The square root of 21106921 is about 4594.2269208214. The cubic root of 21106921 is about 276.3598584374.

The spelling of 21106921 in words is "twenty-one million, one hundred six thousand, nine hundred twenty-one".