21506777215537 has 4 divisors (see below), whose sum is σ = 22638712858480. Its totient is φ = 20374841572596.

The previous prime is 21506777215529. The next prime is 21506777215619. The reversal of 21506777215537 is 73551277760512.

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 a cyclic number.

It is not a de Polignac number, because 21506777215537 - 2³ = 21506777215529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21506777212537) 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, 565967821443 + ... + 565967821480.

It is an arithmetic number, because the mean of its divisors is an integer number (5659678214620).

Almost surely, 2^{21506777215537} is an apocalyptic number.

It is an amenable number.

21506777215537 is a deficient number, since it is larger than the sum of its proper divisors (1131935642943).

21506777215537 is a wasteful number, since it uses less digits than its factorization.

21506777215537 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1131935642942.

The product of its (nonzero) digits is 21609000, while the sum is 58.

The spelling of 21506777215537 in words is "twenty-one trillion, five hundred six billion, seven hundred seventy-seven million, two hundred fifteen thousand, five hundred thirty-seven".