66781421 has 4 divisors (see below), whose sum is σ = 76321632. Its totient is φ = 57241212.

The previous prime is 66781391. The next prime is 66781453. The reversal of 66781421 is 12418766.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12418766 = 2 ⋅6209383.

It is not a de Polignac number, because 66781421 - 2¹⁴ = 66765037 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66781721) 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, 4770095 + ... + 4770108.

It is an arithmetic number, because the mean of its divisors is an integer number (19080408).

Almost surely, 2^66781421 is an apocalyptic number.

It is an amenable number.

66781421 is a deficient number, since it is larger than the sum of its proper divisors (9540211).

66781421 is an equidigital number, since it uses as much as digits as its factorization.

66781421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9540210.

The product of its digits is 16128, while the sum is 35.

The square root of 66781421 is about 8171.9900269151. The cubic root of 66781421 is about 405.7126526878.

The spelling of 66781421 in words is "sixty-six million, seven hundred eighty-one thousand, four hundred twenty-one".