21642140 has 72 divisors (see below), whose sum is σ = 51957360. Its totient is φ = 7547904.

The previous prime is 21642133. The next prime is 21642143. The reversal of 21642140 is 4124612.

21642140 = T₂₈₉ + T₂₉₀ + ... + T₅₃₅.

21642140 = 66² + 67² + ... + 402².

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21642143) 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 23 ways as a sum of consecutive naturals, for example, 64052 + ... + 64388.

It is an arithmetic number, because the mean of its divisors is an integer number (721630).

Almost surely, 2^21642140 is an apocalyptic number.

21642140 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 21642140, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25978680).

21642140 is an abundant number, since it is smaller than the sum of its proper divisors (30315220).

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

21642140 is a wasteful number, since it uses less digits than its factorization.

21642140 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 391 (or 376 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 20.

The square root of 21642140 is about 4652.1113486244. Note that the first 3 decimals coincide. The cubic root of 21642140 is about 278.6763202881.

Adding to 21642140 its reverse (4124612), we get a palindrome (25766752).

The spelling of 21642140 in words is "twenty-one million, six hundred forty-two thousand, one hundred forty".