21187746 has 36 divisors (see below), whose sum is σ = 48778002. Its totient is φ = 6645504.

The previous prime is 21187697. The next prime is 21187753. The reversal of 21187746 is 64778112.

It can be written as a sum of positive squares in 3 ways, for example, as 19053225 + 2134521 = 4365^2 + 1461^2 .

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21187746.

It is an unprimeable number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 3166 + ... + 7238.

Almost surely, 2^21187746 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21187746, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24389001).

21187746 is an abundant number, since it is smaller than the sum of its proper divisors (27590256).

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

21187746 is a wasteful number, since it uses less digits than its factorization.

21187746 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4115 (or 4095 counting only the distinct ones).

The product of its digits is 18816, while the sum is 36.

The square root of 21187746 is about 4603.0148815749. The cubic root of 21187746 is about 276.7121652241.

The spelling of 21187746 in words is "twenty-one million, one hundred eighty-seven thousand, seven hundred forty-six".