21809156 has 12 divisors (see below), whose sum is σ = 38516940. Its totient is φ = 10804320.

The previous prime is 21809153. The next prime is 21809159. The reversal of 21809156 is 65190812.

It is an interprime number because it is at equal distance from previous prime (21809153) and next prime (21809159).

It can be written as a sum of positive squares in 2 ways, for example, as 15132100 + 6677056 = 3890^2 + 2584^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21809153) 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, 24575 + ... + 25446.

It is an arithmetic number, because the mean of its divisors is an integer number (3209745).

Almost surely, 2^21809156 is an apocalyptic number.

It is an amenable number.

21809156 is a deficient number, since it is larger than the sum of its proper divisors (16707784).

21809156 is a wasteful number, since it uses less digits than its factorization.

21809156 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50134 (or 50132 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 32.

The square root of 21809156 is about 4670.0274089131. The cubic root of 21809156 is about 279.3913479649.

Adding to 21809156 its reverse (65190812), we get a palindrome (86999968).

The spelling of 21809156 in words is "twenty-one million, eight hundred nine thousand, one hundred fifty-six".