21781955 has 8 divisors (see below), whose sum is σ = 28149072. Its totient is φ = 16085088.

The previous prime is 21781891. The next prime is 21781967. The reversal of 21781955 is 55918712.

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 21781955 - 2⁶ = 21781891 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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, 167489 + ... + 167618.

It is an arithmetic number, because the mean of its divisors is an integer number (3518634).

Almost surely, 2^21781955 is an apocalyptic number.

21781955 is a deficient number, since it is larger than the sum of its proper divisors (6367117).

21781955 is a wasteful number, since it uses less digits than its factorization.

21781955 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 335125.

The product of its digits is 25200, while the sum is 38.

The square root of 21781955 is about 4667.1142047308. The cubic root of 21781955 is about 279.2751446942.

The spelling of 21781955 in words is "twenty-one million, seven hundred eighty-one thousand, nine hundred fifty-five".