21521177840 has 20 divisors (see below), whose sum is σ = 50036738664. Its totient is φ = 8608471104.

The previous prime is 21521177837. The next prime is 21521177879. The reversal of 21521177840 is 4877112512.

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

It is a super-2 number, since 2×21521177840² (a number of 21 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21521177794 and 21521177803.

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, 134507282 + ... + 134507441.

Almost surely, 2^21521177840 is an apocalyptic number.

21521177840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21521177840 is an abundant number, since it is smaller than the sum of its proper divisors (28515560824).

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

21521177840 is a wasteful number, since it uses less digits than its factorization.

21521177840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 269014736 (or 269014730 counting only the distinct ones).

The product of its (nonzero) digits is 31360, while the sum is 38.

The spelling of 21521177840 in words is "twenty-one billion, five hundred twenty-one million, one hundred seventy-seven thousand, eight hundred forty".