21661344 has 120 divisors (see below), whose sum is σ = 65222388. Its totient is φ = 7050240.

The previous prime is 21661307. The next prime is 21661351. The reversal of 21661344 is 44316612.

21661344 is a `hidden beast` number, since 2 + 1 + 6 + 613 + 44 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 20250000 + 1411344 = 4500^2 + 1188^2 .

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 158044 + ... + 158180.

Almost surely, 2^21661344 is an apocalyptic number.

21661344 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21661344, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32611194).

21661344 is an abundant number, since it is smaller than the sum of its proper divisors (43561044).

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

21661344 is a wasteful number, since it uses less digits than its factorization.

21661344 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 220 (or 203 counting only the distinct ones).

The product of its digits is 3456, while the sum is 27.

The square root of 21661344 is about 4654.1749000226. The cubic root of 21661344 is about 278.7587230742.

Adding to 21661344 its reverse (44316612), we get a palindrome (65977956).

The spelling of 21661344 in words is "twenty-one million, six hundred sixty-one thousand, three hundred forty-four".