21626640 has 180 divisors, whose sum is σ = 84625164. Its totient is φ = 4935168.

The previous prime is 21626621. The next prime is 21626641. The reversal of 21626640 is 4662612.

It is a happy number.

21626640 is a `hidden beast` number, since 2 + 16 + 2 + 6 + 640 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 2547216 + 19079424 = 1596^2 + 4368^2 .

It is a tau number, because it is divible by the number of its divisors (180).

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21626641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 34974 + ... + 35586.

Almost surely, 2^21626640 is an apocalyptic number.

21626640 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 21626640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (42312582).

21626640 is an abundant number, since it is smaller than the sum of its proper divisors (62998524).

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

21626640 is a wasteful number, since it uses less digits than its factorization.

21626640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 646 (or 630 counting only the distinct ones).

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

The square root of 21626640 is about 4650.4451399839. The cubic root of 21626640 is about 278.6097755044.

The spelling of 21626640 in words is "twenty-one million, six hundred twenty-six thousand, six hundred forty".