21315655 has 4 divisors (see below), whose sum is σ = 25578792. Its totient is φ = 17052520.

The previous prime is 21315649. The next prime is 21315661. The reversal of 21315655 is 55651312.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21315649) and next prime (21315661).

It is not a de Polignac number, because 21315655 - 2³ = 21315647 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2131561 + ... + 2131570.

It is an arithmetic number, because the mean of its divisors is an integer number (6394698).

Almost surely, 2^21315655 is an apocalyptic number.

21315655 is a deficient number, since it is larger than the sum of its proper divisors (4263137).

21315655 is an equidigital number, since it uses as much as digits as its factorization.

21315655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4263136.

The product of its digits is 4500, while the sum is 28.

The square root of 21315655 is about 4616.8880211675. Note that the first 3 decimals coincide. The cubic root of 21315655 is about 277.2678793709.

Adding to 21315655 its reverse (55651312), we get a palindrome (76966967).

The spelling of 21315655 in words is "twenty-one million, three hundred fifteen thousand, six hundred fifty-five".