21891971 has 8 divisors (see below), whose sum is σ = 24400080. Its totient is φ = 19519488.

The previous prime is 21891967. The next prime is 21891973. The reversal of 21891971 is 17919812.

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 21891971 - 2² = 21891967 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21891973) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 33566 + ... + 34211.

It is an arithmetic number, because the mean of its divisors is an integer number (3050010).

Almost surely, 2^21891971 is an apocalyptic number.

21891971 is a deficient number, since it is larger than the sum of its proper divisors (2508109).

21891971 is a wasteful number, since it uses less digits than its factorization.

21891971 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 67813.

The product of its digits is 9072, while the sum is 38.

The square root of 21891971 is about 4678.8856579318. The cubic root of 21891971 is about 279.7445416630.

The spelling of 21891971 in words is "twenty-one million, eight hundred ninety-one thousand, nine hundred seventy-one".