21719391 has 16 divisors (see below), whose sum is σ = 29621760. Its totient is φ = 14152320.

The previous prime is 21719389. The next prime is 21719393. The reversal of 21719391 is 19391712.

It is an interprime number because it is at equal distance from previous prime (21719389) and next prime (21719393).

It is not a de Polignac number, because 21719391 - 2¹ = 21719389 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21719393) 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, 26376 + ... + 27186.

It is an arithmetic number, because the mean of its divisors is an integer number (1851360).

Almost surely, 2^21719391 is an apocalyptic number.

21719391 is the 2948-th centered pentagonal number.

21719391 is a deficient number, since it is larger than the sum of its proper divisors (7902369).

21719391 is a wasteful number, since it uses less digits than its factorization.

21719391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1006.

The product of its digits is 3402, while the sum is 33.

The square root of 21719391 is about 4660.4067419057. The cubic root of 21719391 is about 279.0075022713.

The spelling of 21719391 in words is "twenty-one million, seven hundred nineteen thousand, three hundred ninety-one".