21781156 has 24 divisors (see below), whose sum is σ = 39088280. Its totient is φ = 10616832.

The previous prime is 21781139. The next prime is 21781157. The reversal of 21781156 is 65118712.

It can be written as a sum of positive squares in 4 ways, for example, as 2509056 + 19272100 = 1584^2 + 4390^2 .

It is not an unprimeable number, because it can be changed into a prime (21781157) 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, 27940 + ... + 28708.

Almost surely, 2^21781156 is an apocalyptic number.

It is an amenable number.

21781156 is a deficient number, since it is larger than the sum of its proper divisors (17307124).

21781156 is a wasteful number, since it uses less digits than its factorization.

21781156 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 943 (or 941 counting only the distinct ones).

The product of its digits is 3360, while the sum is 31.

The square root of 21781156 is about 4667.0286050120. The cubic root of 21781156 is about 279.2717298864.

Adding to 21781156 its reverse (65118712), we get a palindrome (86899868).

The spelling of 21781156 in words is "twenty-one million, seven hundred eighty-one thousand, one hundred fifty-six".