21891023 has 16 divisors (see below), whose sum is σ = 27558144. Its totient is φ = 16892160.

The previous prime is 21890993. The next prime is 21891029. The reversal of 21891023 is 32019812.

21891023 = T₁₉₇ + T₁₉₈ + ... + T₅₁₇.

21891023 = 987² + 988² + ... + 1008².

It is a cyclic number.

It is not a de Polignac number, because 21891023 - 2⁶ = 21890959 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21890983 and 21891001.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21891029) 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, 6911 + ... + 9567.

It is an arithmetic number, because the mean of its divisors is an integer number (1722384).

Almost surely, 2^21891023 is an apocalyptic number.

21891023 is a deficient number, since it is larger than the sum of its proper divisors (5667121).

21891023 is a wasteful number, since it uses less digits than its factorization.

21891023 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2782.

The product of its (nonzero) digits is 864, while the sum is 26.

The square root of 21891023 is about 4678.7843506620. The cubic root of 21891023 is about 279.7405036277.

The spelling of 21891023 in words is "twenty-one million, eight hundred ninety-one thousand, twenty-three".