21001555155 has 32 divisors (see below), whose sum is σ = 38865544704. Its totient is φ = 9485035776.

The previous prime is 21001555111. The next prime is 21001555177. The reversal of 21001555155 is 55155510012.

It is not a de Polignac number, because 21001555155 - 2⁹ = 21001554643 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1196194 + ... + 1213623.

It is an arithmetic number, because the mean of its divisors is an integer number (1214548272).

Almost surely, 2^21001555155 is an apocalyptic number.

21001555155 is a deficient number, since it is larger than the sum of its proper divisors (17863989549).

21001555155 is a wasteful number, since it uses less digits than its factorization.

21001555155 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2409915.

The product of its (nonzero) digits is 6250, while the sum is 30.

The spelling of 21001555155 in words is "twenty-one billion, one million, five hundred fifty-five thousand, one hundred fifty-five".