21690144 has 216 divisors, whose sum is σ = 75626460. Its totient is φ = 5870592.

The previous prime is 21690143. The next prime is 21690157. The reversal of 21690144 is 44109612.

It can be written as a sum of positive squares in 2 ways, for example, as 21344400 + 345744 = 4620^2 + 588^2 .

It is not an unprimeable number, because it can be changed into a prime (21690143) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 409222 + ... + 409274.

Almost surely, 2^21690144 is an apocalyptic number.

21690144 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 21690144, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37813230).

21690144 is an abundant number, since it is smaller than the sum of its proper divisors (53936316).

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

21690144 is a wasteful number, since it uses less digits than its factorization.

21690144 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 112 (or 94 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21690144 is about 4657.2678686114. The cubic root of 21690144 is about 278.8822102694.

Adding to 21690144 its reverse (44109612), we get a palindrome (65799756).

The spelling of 21690144 in words is "twenty-one million, six hundred ninety thousand, one hundred forty-four".