21405118509 has 16 divisors (see below), whose sum is σ = 31736971840. Its totient is φ = 14258520720.

The previous prime is 21405118459. The next prime is 21405118547. The reversal of 21405118509 is 90581150412.

21405118509 is a `hidden beast` number, since 2 + 140 + 5 + 1 + 1 + 8 + 509 = 666.

It is not a de Polignac number, because 21405118509 - 2¹² = 21405114413 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 (21405118549) 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, 287047 + ... + 353844.

It is an arithmetic number, because the mean of its divisors is an integer number (1983560740).

Almost surely, 2^21405118509 is an apocalyptic number.

It is an amenable number.

21405118509 is a deficient number, since it is larger than the sum of its proper divisors (10331853331).

21405118509 is a wasteful number, since it uses less digits than its factorization.

21405118509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 642137 (or 642131 counting only the distinct ones).

The product of its (nonzero) digits is 14400, while the sum is 36.

The spelling of 21405118509 in words is "twenty-one billion, four hundred five million, one hundred eighteen thousand, five hundred nine".