21765740 has 24 divisors (see below), whose sum is σ = 46772880. Its totient is φ = 8503488.

The previous prime is 21765719. The next prime is 21765743. The reversal of 21765740 is 4756712.

It is a junction number, because it is equal to n+sod(n) for n = 21765697 and 21765706.

It is not an unprimeable number, because it can be changed into a prime (21765743) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11795 + ... + 13514.

It is an arithmetic number, because the mean of its divisors is an integer number (1948870).

Almost surely, 2^21765740 is an apocalyptic number.

21765740 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21765740 is an abundant number, since it is smaller than the sum of its proper divisors (25007140).

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

21765740 is a wasteful number, since it uses less digits than its factorization.

21765740 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25361 (or 25359 counting only the distinct ones).

The product of its (nonzero) digits is 11760, while the sum is 32.

The square root of 21765740 is about 4665.3767264820. The cubic root of 21765740 is about 279.2058278272.

Subtracting from 21765740 its reverse (4756712), we obtain a triangular number (17009028 = T₅₈₃₂).

The spelling of 21765740 in words is "twenty-one million, seven hundred sixty-five thousand, seven hundred forty".