21813156 has 18 divisors (see below), whose sum is σ = 55138902. Its totient is φ = 7271040.

The previous prime is 21813101. The next prime is 21813163. The reversal of 21813156 is 65131812.

It can be written as a sum of positive squares in only one way, i.e., 14062500 + 7750656 = 3750^2 + 2784^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a congruent 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 5 ways as a sum of consecutive naturals, for example, 302925 + ... + 302996.

Almost surely, 2^21813156 is an apocalyptic number.

It is an amenable number.

21813156 is an abundant number, since it is smaller than the sum of its proper divisors (33325746).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21813156 is a wasteful number, since it uses less digits than its factorization.

21813156 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 605931 (or 605926 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 21813156 is about 4670.4556522892. The cubic root of 21813156 is about 279.4084279026.

Adding to 21813156 its reverse (65131812), we get a palindrome (86944968).

The spelling of 21813156 in words is "twenty-one million, eight hundred thirteen thousand, one hundred fifty-six".