21643506 has 36 divisors (see below), whose sum is σ = 49043358. Its totient is φ = 6897792.

The previous prime is 21643429. The next prime is 21643507. The reversal of 21643506 is 60534612.

It can be written as a sum of positive squares in only one way, i.e., 14402025 + 7241481 = 3795^2 + 2691^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21643506.

It is not an unprimeable number, because it can be changed into a prime (21643507) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 8386 + ... + 10658.

Almost surely, 2^21643506 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21643506, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24521679).

21643506 is an abundant number, since it is smaller than the sum of its proper divisors (27399852).

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

21643506 is a wasteful number, since it uses less digits than its factorization.

21643506 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2327 (or 2301 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 27.

The square root of 21643506 is about 4652.2581613664. The cubic root of 21643506 is about 278.6821832918.

The spelling of 21643506 in words is "twenty-one million, six hundred forty-three thousand, five hundred six".