21505634477 has 4 divisors (see below), whose sum is σ = 21963201216. Its totient is φ = 21048067740.

The previous prime is 21505634471. The next prime is 21505634489. The reversal of 21505634477 is 77443650512.

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 21505634477 - 2¹² = 21505630381 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505634471) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 228783299 + ... + 228783392.

It is an arithmetic number, because the mean of its divisors is an integer number (5490800304).

Almost surely, 2^21505634477 is an apocalyptic number.

It is an amenable number.

21505634477 is a deficient number, since it is larger than the sum of its proper divisors (457566739).

21505634477 is an equidigital number, since it uses as much as digits as its factorization.

21505634477 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 457566738.

The product of its (nonzero) digits is 705600, while the sum is 44.

The spelling of 21505634477 in words is "twenty-one billion, five hundred five million, six hundred thirty-four thousand, four hundred seventy-seven".