21555013221 has 48 divisors (see below), whose sum is σ = 37179814080. Its totient is φ = 12306258720.

The previous prime is 21555013199. The next prime is 21555013243. The reversal of 21555013221 is 12231055512.

21555013221 is a `hidden beast` number, since 2 + 155 + 501 + 3 + 2 + 2 + 1 = 666.

It is an interprime number because it is at equal distance from previous prime (21555013199) and next prime (21555013243).

It is not a de Polignac number, because 21555013221 - 2⁶ = 21555013157 is a prime.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21555013261) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1629966 + ... + 1643136.

It is an arithmetic number, because the mean of its divisors is an integer number (774579460).

Almost surely, 2^21555013221 is an apocalyptic number.

21555013221 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21555013221 is a deficient number, since it is larger than the sum of its proper divisors (15624800859).

21555013221 is a wasteful number, since it uses less digits than its factorization.

21555013221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14431 (or 14418 counting only the distinct ones).

The product of its (nonzero) digits is 3000, while the sum is 27.

Adding to 21555013221 its reverse (12231055512), we get a palindrome (33786068733).

The spelling of 21555013221 in words is "twenty-one billion, five hundred fifty-five million, thirteen thousand, two hundred twenty-one".