21555207121 has 4 divisors (see below), whose sum is σ = 24634522432. Its totient is φ = 18475891812.

The previous prime is 21555207109. The next prime is 21555207133. The reversal of 21555207121 is 12170255512.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (21555207109) and next prime (21555207133).

It is not a de Polignac number, because 21555207121 - 2⁹ = 21555206609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21555207151) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1539657645 + ... + 1539657658.

It is an arithmetic number, because the mean of its divisors is an integer number (6158630608).

Almost surely, 2^21555207121 is an apocalyptic number.

It is an amenable number.

21555207121 is a deficient number, since it is larger than the sum of its proper divisors (3079315311).

21555207121 is an equidigital number, since it uses as much as digits as its factorization.

21555207121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3079315310.

The product of its (nonzero) digits is 7000, while the sum is 31.

The spelling of 21555207121 in words is "twenty-one billion, five hundred fifty-five million, two hundred seven thousand, one hundred twenty-one".