21638340 has 180 divisors, whose sum is σ = 73577196. Its totient is φ = 5318784.

The previous prime is 21638339. The next prime is 21638371. The reversal of 21638340 is 4383612.

It is a happy number.

21638340 is a `hidden beast` number, since 21 + 638 + 3 + 4 + 0 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 14152644 + 7485696 = 3762^2 + 2736^2 .

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

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

It is an unprimeable number.

It is a polite number, since it can be written in 59 ways as a sum of consecutive naturals, for example, 584802 + ... + 584838.

Almost surely, 2^21638340 is an apocalyptic number.

21638340 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 21638340, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36788598).

21638340 is an abundant number, since it is smaller than the sum of its proper divisors (51938856).

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

21638340 is a wasteful number, since it uses less digits than its factorization.

21638340 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 96 (or 66 counting only the distinct ones).

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

The square root of 21638340 is about 4651.7029139875. The cubic root of 21638340 is about 278.6600090237.

The spelling of 21638340 in words is "twenty-one million, six hundred thirty-eight thousand, three hundred forty".