21537781440 has 672 divisors, whose sum is σ = 87963231744. Its totient is φ = 4428103680.

The previous prime is 21537781411. The next prime is 21537781459. The reversal of 21537781440 is 4418773512.

It is a tau number, because it is divible by the number of its divisors (672).

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a junction number, because it is equal to n+sod(n) for n = 21537781392 and 21537781401.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 18392055 + ... + 18393225.

Almost surely, 2^21537781440 is an apocalyptic number.

21537781440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21537781440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (43981615872).

21537781440 is an abundant number, since it is smaller than the sum of its proper divisors (66425450304).

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

21537781440 is a wasteful number, since it uses less digits than its factorization.

21537781440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1245 (or 1228 counting only the distinct ones).

The product of its (nonzero) digits is 188160, while the sum is 42.

The spelling of 21537781440 in words is "twenty-one billion, five hundred thirty-seven million, seven hundred eighty-one thousand, four hundred forty".