21056505155 has 12 divisors (see below), whose sum is σ = 29393162640. Its totient is φ = 14438746224.

The previous prime is 21056505143. The next prime is 21056505163. The reversal of 21056505155 is 55150565012.

It is a happy number.

It is not a de Polignac number, because 21056505155 - 2²⁰ = 21055456579 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (35).

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 42972215 + ... + 42972704.

It is an arithmetic number, because the mean of its divisors is an integer number (2449430220).

Almost surely, 2^21056505155 is an apocalyptic number.

21056505155 is a deficient number, since it is larger than the sum of its proper divisors (8336657485).

21056505155 is an equidigital number, since it uses as much as digits as its factorization.

21056505155 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 85944938 (or 85944931 counting only the distinct ones).

The product of its (nonzero) digits is 37500, while the sum is 35.

The spelling of 21056505155 in words is "twenty-one billion, fifty-six million, five hundred five thousand, one hundred fifty-five".