21018810506 has 8 divisors (see below), whose sum is σ = 33382816740. Its totient is φ = 9891204928.

The previous prime is 21018810493. The next prime is 21018810509. The reversal of 21018810506 is 60501881012.

It can be written as a sum of positive squares in 2 ways, for example, as 17593634881 + 3425175625 = 132641^2 + 58525^2 .

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

It is not an unprimeable number, because it can be changed into a prime (21018810509) 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, 309100121 + ... + 309100188.

Almost surely, 2^21018810506 is an apocalyptic number.

21018810506 is a deficient number, since it is larger than the sum of its proper divisors (12364006234).

21018810506 is a wasteful number, since it uses less digits than its factorization.

21018810506 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 618200328.

The product of its (nonzero) digits is 3840, while the sum is 32.

The spelling of 21018810506 in words is "twenty-one billion, eighteen million, eight hundred ten thousand, five hundred six".