21455991 has 6 divisors (see below), whose sum is σ = 30992000. Its totient is φ = 14303988.

The previous prime is 21455983. The next prime is 21456007. The reversal of 21455991 is 19955412.

21455991 is a `hidden beast` number, since 2 + 14 + 559 + 91 = 666.

It is not a de Polignac number, because 21455991 - 2³ = 21455983 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21455971) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1191991 + ... + 1192008.

Almost surely, 2^21455991 is an apocalyptic number.

21455991 is a deficient number, since it is larger than the sum of its proper divisors (9536009).

21455991 is a wasteful number, since it uses less digits than its factorization.

21455991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2384005 (or 2384002 counting only the distinct ones).

The product of its digits is 16200, while the sum is 36.

The square root of 21455991 is about 4632.0612042589. The cubic root of 21455991 is about 277.8750322509.

The spelling of 21455991 in words is "twenty-one million, four hundred fifty-five thousand, nine hundred ninety-one".