21205520545 has 16 divisors (see below), whose sum is σ = 28019400768. Its totient is φ = 15278059840.

The previous prime is 21205520543. The next prime is 21205520573. The reversal of 21205520545 is 54502550212.

It is a happy number.

It is not a de Polignac number, because 21205520545 - 2¹ = 21205520543 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21205520543) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1795774 + ... + 1807543.

It is an arithmetic number, because the mean of its divisors is an integer number (1751212548).

Almost surely, 2^21205520545 is an apocalyptic number.

It is an amenable number.

21205520545 is a deficient number, since it is larger than the sum of its proper divisors (6813880223).

21205520545 is a wasteful number, since it uses less digits than its factorization.

21205520545 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3603440.

The product of its (nonzero) digits is 20000, while the sum is 31.

The spelling of 21205520545 in words is "twenty-one billion, two hundred five million, five hundred twenty thousand, five hundred forty-five".