21505400240 has 20 divisors (see below), whose sum is σ = 50000055744. Its totient is φ = 8602160064.

The previous prime is 21505400239. The next prime is 21505400281. The reversal of 21505400240 is 4200450512.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (20).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 134408672 + ... + 134408831.

Almost surely, 2^21505400240 is an apocalyptic number.

21505400240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21505400240 is an abundant number, since it is smaller than the sum of its proper divisors (28494655504).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21505400240 is a wasteful number, since it uses less digits than its factorization.

21505400240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 268817516 (or 268817510 counting only the distinct ones).

The product of its (nonzero) digits is 1600, while the sum is 23.

Adding to 21505400240 its reverse (4200450512), we get a palindrome (25705850752).

The spelling of 21505400240 in words is "twenty-one billion, five hundred five million, four hundred thousand, two hundred forty".