21851381 has 4 divisors (see below), whose sum is σ = 22316352. Its totient is φ = 21386412.

The previous prime is 21851377. The next prime is 21851383. The reversal of 21851381 is 18315812.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21851381 - 2² = 21851377 is a prime.

It is a super-2 number, since 2×21851381² = 954965703214322, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21851383) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 232415 + ... + 232508.

It is an arithmetic number, because the mean of its divisors is an integer number (5579088).

Almost surely, 2^21851381 is an apocalyptic number.

It is an amenable number.

21851381 is a deficient number, since it is larger than the sum of its proper divisors (464971).

21851381 is an equidigital number, since it uses as much as digits as its factorization.

21851381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 464970.

The product of its digits is 1920, while the sum is 29.

The square root of 21851381 is about 4674.5460742194. The cubic root of 21851381 is about 279.5715428367.

The spelling of 21851381 in words is "twenty-one million, eight hundred fifty-one thousand, three hundred eighty-one".