21791687 has 2 divisors, whose sum is σ = 21791688. Its totient is φ = 21791686.

The previous prime is 21791681. The next prime is 21791699. The reversal of 21791687 is 78619712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21791687 - 2¹⁶ = 21726151 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21791681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10895843 + 10895844.

It is an arithmetic number, because the mean of its divisors is an integer number (10895844).

Almost surely, 2^21791687 is an apocalyptic number.

21791687 is a deficient number, since it is larger than the sum of its proper divisors (1).

21791687 is an equidigital number, since it uses as much as digits as its factorization.

21791687 is an evil number, because the sum of its binary digits is even.

The product of its digits is 42336, while the sum is 41.

The square root of 21791687 is about 4668.1567025969. The cubic root of 21791687 is about 279.3167311209.

The spelling of 21791687 in words is "twenty-one million, seven hundred ninety-one thousand, six hundred eighty-seven".