21897940 has 12 divisors (see below), whose sum is σ = 45985716. Its totient is φ = 8759168.

The previous prime is 21897913. The next prime is 21897949. The reversal of 21897940 is 4979812.

It can be written as a sum of positive squares in 2 ways, for example, as 15272464 + 6625476 = 3908^2 + 2574^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21897893 and 21897902.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21897949) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 547429 + ... + 547468.

It is an arithmetic number, because the mean of its divisors is an integer number (3832143).

Almost surely, 2^21897940 is an apocalyptic number.

21897940 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21897940 is an abundant number, since it is smaller than the sum of its proper divisors (24087776).

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

21897940 is a wasteful number, since it uses less digits than its factorization.

21897940 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1094906 (or 1094904 counting only the distinct ones).

The product of its (nonzero) digits is 36288, while the sum is 40.

The square root of 21897940 is about 4679.5234800138. The cubic root of 21897940 is about 279.7699641255.

The spelling of 21897940 in words is "twenty-one million, eight hundred ninety-seven thousand, nine hundred forty".