21555191 has 8 divisors (see below), whose sum is σ = 24783360. Its totient is φ = 18364248.

The previous prime is 21555181. The next prime is 21555197. The reversal of 21555191 is 19155512.

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

It is a de Polignac number, because none of the positive numbers 2^k-21555191 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21555197) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8051 + ... + 10388.

It is an arithmetic number, because the mean of its divisors is an integer number (3097920).

Almost surely, 2^21555191 is an apocalyptic number.

21555191 is a deficient number, since it is larger than the sum of its proper divisors (3228169).

21555191 is a wasteful number, since it uses less digits than its factorization.

21555191 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18613.

The product of its digits is 2250, while the sum is 29.

The square root of 21555191 is about 4642.7568318834. The cubic root of 21555191 is about 278.3026180344.

The spelling of 21555191 in words is "twenty-one million, five hundred fifty-five thousand, one hundred ninety-one".