21651000 has 128 divisors (see below), whose sum is σ = 77276160. Its totient is φ = 4944000.

The previous prime is 21650999. The next prime is 21651011. The reversal of 21651000 is 15612.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 20485 + ... + 21515.

It is an arithmetic number, because the mean of its divisors is an integer number (603720).

Almost surely, 2^21651000 is an apocalyptic number.

21651000 is a gapful number since it is divisible by the number (20) 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 21651000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38638080).

21651000 is an abundant number, since it is smaller than the sum of its proper divisors (55625160).

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

21651000 is a wasteful number, since it uses less digits than its factorization.

21651000 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1062 (or 1048 counting only the distinct ones).

The product of its (nonzero) digits is 60, while the sum is 15.

The square root of 21651000 is about 4653.0635069812. The cubic root of 21651000 is about 278.7143438744.

Adding to 21651000 its reverse (15612), we get a palindrome (21666612).

The spelling of 21651000 in words is "twenty-one million, six hundred fifty-one thousand".