21397680 has 120 divisors (see below), whose sum is σ = 72772128. Its totient is φ = 5634048.

The previous prime is 21397669. The next prime is 21397693. The reversal of 21397680 is 8679312.

It is a tau number, because it is divible by the number of its divisors (120).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 81229 + ... + 81491.

Almost surely, 2^21397680 is an apocalyptic number.

21397680 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 21397680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36386064).

21397680 is an abundant number, since it is smaller than the sum of its proper divisors (51374448).

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

21397680 is a wasteful number, since it uses less digits than its factorization.

21397680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 395 (or 386 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 36.

The square root of 21397680 is about 4625.7626398249. The cubic root of 21397680 is about 277.6230766444.

The spelling of 21397680 in words is "twenty-one million, three hundred ninety-seven thousand, six hundred eighty".