21781968 has 80 divisors (see below), whose sum is σ = 61621056. Its totient is φ = 6589440.

The previous prime is 21781967. The next prime is 21781979. The reversal of 21781968 is 86918712.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21781967) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 41548 + ... + 42068.

Almost surely, 2^21781968 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21781968, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30810528).

21781968 is an abundant number, since it is smaller than the sum of its proper divisors (39839088).

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

21781968 is a wasteful number, since it uses less digits than its factorization.

21781968 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 612 (or 606 counting only the distinct ones).

The product of its digits is 48384, while the sum is 42.

The square root of 21781968 is about 4667.1155974542. The cubic root of 21781968 is about 279.2752002536.

The spelling of 21781968 in words is "twenty-one million, seven hundred eighty-one thousand, nine hundred sixty-eight".