21661838 has 16 divisors (see below), whose sum is σ = 35876736. Its totient is φ = 9726840.

The previous prime is 21661831. The next prime is 21661841. The reversal of 21661838 is 83816612.

It is a junction number, because it is equal to n+sod(n) for n = 21661798 and 21661807.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661831) 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, 4106 + ... + 7757.

It is an arithmetic number, because the mean of its divisors is an integer number (2242296).

Almost surely, 2^21661838 is an apocalyptic number.

21661838 is a deficient number, since it is larger than the sum of its proper divisors (14214898).

21661838 is a wasteful number, since it uses less digits than its factorization.

21661838 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11959.

The product of its digits is 13824, while the sum is 35.

The square root of 21661838 is about 4654.2279703513. The cubic root of 21661838 is about 278.7608421450.

It can be divided in two parts, 2166 and 1838, that added together give a palindrome (4004).

The spelling of 21661838 in words is "twenty-one million, six hundred sixty-one thousand, eight hundred thirty-eight".