21997560 has 128 divisors (see below), whose sum is σ = 72576000. Its totient is φ = 5300736.

The previous prime is 21997531. The next prime is 21997567. The reversal of 21997560 is 6579912.

It is a super-3 number, since 3×21997560³ (a number of 23 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21997567) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 91921 + ... + 92159.

It is an arithmetic number, because the mean of its divisors is an integer number (567000).

Almost surely, 2^21997560 is an apocalyptic number.

21997560 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 21997560, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36288000).

21997560 is an abundant number, since it is smaller than the sum of its proper divisors (50578440).

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

21997560 is a wasteful number, since it uses less digits than its factorization.

21997560 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 325 (or 321 counting only the distinct ones).

The product of its (nonzero) digits is 34020, while the sum is 39.

The square root of 21997560 is about 4690.1556477371. The cubic root of 21997560 is about 280.1935736280.

It can be divided in two parts, 219 and 97560, that added together give a palindrome (97779).

The spelling of 21997560 in words is "twenty-one million, nine hundred ninety-seven thousand, five hundred sixty".