21051688464 has 135 divisors (see below), whose sum is σ = 60002198893. Its totient is φ = 6890128896.

The previous prime is 21051688433. The next prime is 21051688477. The reversal of 21051688464 is 46488615012.

It is a happy number.

The square root of 21051688464 is 145092.

It is a perfect power (a square), and thus also a powerful number.

21051688464 is a `hidden beast` number, since 2 + 10 + 516 + 88 + 46 + 4 = 666.

It can be written as a sum of positive squares in only one way, i.e., 370947600 + 20680740864 = 19260^2 + 143808^2 .

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 186298072 + ... + 186298184.

Almost surely, 2^21051688464 is an apocalyptic number.

21051688464 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

21051688464 is the 145092-nd square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21051688464

21051688464 is an abundant number, since it is smaller than the sum of its proper divisors (38950510429).

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

21051688464 is a wasteful number, since it uses less digits than its factorization.

21051688464 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 454 (or 225 counting only the distinct ones).

The product of its (nonzero) digits is 368640, while the sum is 45.

The spelling of 21051688464 in words is "twenty-one billion, fifty-one million, six hundred eighty-eight thousand, four hundred sixty-four".