66921840 has 120 divisors (see below), whose sum is σ = 230329008. Its totient is φ = 17402880.

The previous prime is 66921791. The next prime is 66921847. The reversal of 66921840 is 4812966.

It is a tau number, because it is divible by the number of its divisors (120).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 66921795 and 66921804.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66921847) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 28387 + ... + 30653.

Almost surely, 2^66921840 is an apocalyptic number.

66921840 is a gapful number since it is divisible by the number (60) 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 66921840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (115164504).

66921840 is an abundant number, since it is smaller than the sum of its proper divisors (163407168).

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

66921840 is a wasteful number, since it uses less digits than its factorization.

66921840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2327 (or 2318 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 36.

The square root of 66921840 is about 8180.5769967650. The cubic root of 66921840 is about 405.9968129689.

The spelling of 66921840 in words is "sixty-six million, nine hundred twenty-one thousand, eight hundred forty".