21181680 has 240 divisors, whose sum is σ = 80161536. Its totient is φ = 4976640.

The previous prime is 21181679. The next prime is 21181697. The reversal of 21181680 is 8618112.

It is a tau number, because it is divible by the number of its divisors (240).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 290124 + ... + 290196.

Almost surely, 2^21181680 is an apocalyptic number.

21181680 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 21181680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40080768).

21181680 is an abundant number, since it is smaller than the sum of its proper divisors (58979856).

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

21181680 is a wasteful number, since it uses less digits than its factorization.

21181680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 136 (or 127 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 27.

The square root of 21181680 is about 4602.3559184400. The cubic root of 21181680 is about 276.6857553643.

Adding to 21181680 its reverse (8618112), we get a palindrome (29799792).

The spelling of 21181680 in words is "twenty-one million, one hundred eighty-one thousand, six hundred eighty".