21851181 has 64 divisors (see below), whose sum is σ = 38016000. Its totient is φ = 12277440.

The previous prime is 21851177. The next prime is 21851183. The reversal of 21851181 is 18115812.

It is not a de Polignac number, because 21851181 - 2² = 21851177 is a prime.

It is a super-2 number, since 2×21851181² = 954948222189522, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21851183) by changing a digit.

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 63 ways as a sum of consecutive naturals, for example, 370330 + ... + 370388.

It is an arithmetic number, because the mean of its divisors is an integer number (594000).

Almost surely, 2^21851181 is an apocalyptic number.

It is an amenable number.

21851181 is a deficient number, since it is larger than the sum of its proper divisors (16164819).

21851181 is a wasteful number, since it uses less digits than its factorization.

21851181 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 151 (or 145 counting only the distinct ones).

The product of its digits is 640, while the sum is 27.

The square root of 21851181 is about 4674.5246817190. The cubic root of 21851181 is about 279.5706898856.

Adding to 21851181 its reverse (18115812), we get a palindrome (39966993).

The spelling of 21851181 in words is "twenty-one million, eight hundred fifty-one thousand, one hundred eighty-one".