21688738 has 16 divisors (see below), whose sum is σ = 33233400. Its totient is φ = 10613376.

The previous prime is 21688729. The next prime is 21688741. The reversal of 21688738 is 83788612.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 18774889 + 2913849 = 4333^2 + 1707^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21688694 and 21688703.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21256 + ... + 22252.

Almost surely, 2^21688738 is an apocalyptic number.

21688738 is a deficient number, since it is larger than the sum of its proper divisors (11544662).

21688738 is a wasteful number, since it uses less digits than its factorization.

21688738 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1221.

The product of its digits is 129024, while the sum is 43.

The square root of 21688738 is about 4657.1169192967. The cubic root of 21688738 is about 278.8761842320.

The spelling of 21688738 in words is "twenty-one million, six hundred eighty-eight thousand, seven hundred thirty-eight".