21506438840 has 16 divisors (see below), whose sum is σ = 48389487480. Its totient is φ = 8602575520.

The previous prime is 21506438839. The next prime is 21506438861. The reversal of 21506438840 is 4883460512.

It is a congruent number.

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, 268830446 + ... + 268830525.

Almost surely, 2^21506438840 is an apocalyptic number.

21506438840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21506438840 is an abundant number, since it is smaller than the sum of its proper divisors (26883048640).

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

21506438840 is a wasteful number, since it uses less digits than its factorization.

21506438840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 537660982 (or 537660978 counting only the distinct ones).

The product of its (nonzero) digits is 184320, while the sum is 41.

The spelling of 21506438840 in words is "twenty-one billion, five hundred six million, four hundred thirty-eight thousand, eight hundred forty".