21006935521 has 16 divisors (see below), whose sum is σ = 25281422208. Its totient is φ = 17198236800.

The previous prime is 21006935519. The next prime is 21006935533. The reversal of 21006935521 is 12553960012.

It is a cyclic number.

It is not a de Polignac number, because 21006935521 - 2¹ = 21006935519 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21006935321) 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, 1785621 + ... + 1797346.

It is an arithmetic number, because the mean of its divisors is an integer number (1580088888).

Almost surely, 2^21006935521 is an apocalyptic number.

It is an amenable number.

21006935521 is a deficient number, since it is larger than the sum of its proper divisors (4274486687).

21006935521 is a wasteful number, since it uses less digits than its factorization.

21006935521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3583032.

The product of its (nonzero) digits is 16200, while the sum is 34.

The spelling of 21006935521 in words is "twenty-one billion, six million, nine hundred thirty-five thousand, five hundred twenty-one".