21395991 has 8 divisors (see below), whose sum is σ = 28635120. Its totient is φ = 14210432.

The previous prime is 21395987. The next prime is 21395999. The reversal of 21395991 is 19959312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21395991 - 2² = 21395987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21395999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12450 + ... + 14063.

It is an arithmetic number, because the mean of its divisors is an integer number (3579390).

Almost surely, 2^21395991 is an apocalyptic number.

21395991 is a deficient number, since it is larger than the sum of its proper divisors (7239129).

21395991 is a wasteful number, since it uses less digits than its factorization.

21395991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26785.

The product of its digits is 21870, while the sum is 39.

The square root of 21395991 is about 4625.5800717315. The cubic root of 21395991 is about 277.6157718382.

The spelling of 21395991 in words is "twenty-one million, three hundred ninety-five thousand, nine hundred ninety-one".