21006655 has 8 divisors (see below), whose sum is σ = 25635600. Its totient is φ = 16520256.

The previous prime is 21006641. The next prime is 21006673. The reversal of 21006655 is 55660012.

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 21006655 - 2¹⁹ = 20482367 is a prime.

It is a congruent number.

It is an unprimeable number.

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, 35310 + ... + 35899.

It is an arithmetic number, because the mean of its divisors is an integer number (3204450).

Almost surely, 2^21006655 is an apocalyptic number.

21006655 is a deficient number, since it is larger than the sum of its proper divisors (4628945).

21006655 is an equidigital number, since it uses as much as digits as its factorization.

21006655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 71273.

The product of its (nonzero) digits is 1800, while the sum is 25.

The square root of 21006655 is about 4583.3017574670. The cubic root of 21006655 is about 275.9215584337.

Adding to 21006655 its reverse (55660012), we get a palindrome (76666667).

The spelling of 21006655 in words is "twenty-one million, six thousand, six hundred fifty-five".