21805506977 has 8 divisors (see below), whose sum is σ = 23326208136. Its totient is φ = 20311252992.

The previous prime is 21805506973. The next prime is 21805507001. The reversal of 21805506977 is 77960550812.

It can be written as a sum of positive squares in 4 ways, for example, as 11693394496 + 10112112481 = 108136^2 + 100559^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21805506977 - 2² = 21805506973 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21805506973) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6610088 + ... + 6613385.

It is an arithmetic number, because the mean of its divisors is an integer number (2915776017).

Almost surely, 2^21805506977 is an apocalyptic number.

It is an amenable number.

21805506977 is a deficient number, since it is larger than the sum of its proper divisors (1520701159).

21805506977 is a wasteful number, since it uses less digits than its factorization.

21805506977 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13223587.

The product of its (nonzero) digits is 1058400, while the sum is 50.

The spelling of 21805506977 in words is "twenty-one billion, eight hundred five million, five hundred six thousand, nine hundred seventy-seven".