21155506 has 8 divisors (see below), whose sum is σ = 32060700. Its totient is φ = 10468608.

The previous prime is 21155503. The next prime is 21155507. The reversal of 21155506 is 60555112.

It can be written as a sum of positive squares in 2 ways, for example, as 17766225 + 3389281 = 4215^2 + 1841^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not an unprimeable number, because it can be changed into a prime (21155501) 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, 54331 + ... + 54718.

Almost surely, 2^21155506 is an apocalyptic number.

21155506 is a deficient number, since it is larger than the sum of its proper divisors (10905194).

21155506 is a wasteful number, since it uses less digits than its factorization.

21155506 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109148.

The product of its (nonzero) digits is 1500, while the sum is 25.

The square root of 21155506 is about 4599.5114958004. The cubic root of 21155506 is about 276.5717424066.

The spelling of 21155506 in words is "twenty-one million, one hundred fifty-five thousand, five hundred six".