66400921 has 4 divisors (see below), whose sum is σ = 66448692. Its totient is φ = 66353152.

The previous prime is 66400897. The next prime is 66400933. The reversal of 66400921 is 12900466.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 42771600 + 23629321 = 6540^2 + 4861^2 .

It is a cyclic number.

It is not a de Polignac number, because 66400921 - 2⁵ = 66400889 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 66400921.

It is not an unprimeable number, because it can be changed into a prime (66400951) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21736 + ... + 24601.

It is an arithmetic number, because the mean of its divisors is an integer number (16612173).

Almost surely, 2^66400921 is an apocalyptic number.

It is an amenable number.

66400921 is a deficient number, since it is larger than the sum of its proper divisors (47771).

66400921 is a wasteful number, since it uses less digits than its factorization.

66400921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 47770.

The product of its (nonzero) digits is 2592, while the sum is 28.

The square root of 66400921 is about 8148.6760274292. The cubic root of 66400921 is about 404.9406426244.

The spelling of 66400921 in words is "sixty-six million, four hundred thousand, nine hundred twenty-one".