21012155 has 8 divisors (see below), whose sum is σ = 25239600. Its totient is φ = 16793056.

The previous prime is 21012151. The next prime is 21012161. The reversal of 21012155 is 55121012.

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

It is a cyclic number.

It is not a de Polignac number, because 21012155 - 2² = 21012151 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21012151) 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 7 ways as a sum of consecutive naturals, for example, 7316 + ... + 9774.

It is an arithmetic number, because the mean of its divisors is an integer number (3154950).

Almost surely, 2^21012155 is an apocalyptic number.

21012155 is a deficient number, since it is larger than the sum of its proper divisors (4227445).

21012155 is a wasteful number, since it uses less digits than its factorization.

21012155 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4173.

The product of its (nonzero) digits is 100, while the sum is 17.

The square root of 21012155 is about 4583.9017223322. The cubic root of 21012155 is about 275.9456370911.

Adding to 21012155 its reverse (55121012), we get a palindrome (76133167).

The spelling of 21012155 in words is "twenty-one million, twelve thousand, one hundred fifty-five".