21153555 has 40 divisors (see below), whose sum is σ = 39930000. Its totient is φ = 10684224.

The previous prime is 21153551. The next prime is 21153571. The reversal of 21153555 is 55535112.

It is not a de Polignac number, because 21153555 - 2² = 21153551 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21153551) 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 39 ways as a sum of consecutive naturals, for example, 6321 + ... + 9069.

It is an arithmetic number, because the mean of its divisors is an integer number (998250).

Almost surely, 2^21153555 is an apocalyptic number.

21153555 is a deficient number, since it is larger than the sum of its proper divisors (18776445).

21153555 is a wasteful number, since it uses less digits than its factorization.

21153555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2785 (or 2776 counting only the distinct ones).

The product of its digits is 3750, while the sum is 27.

The square root of 21153555 is about 4599.2994031700. The cubic root of 21153555 is about 276.5632401589.

Adding to 21153555 its reverse (55535112), we get a palindrome (76688667).

The spelling of 21153555 in words is "twenty-one million, one hundred fifty-three thousand, five hundred fifty-five".