66655621 has 4 divisors (see below), whose sum is σ = 66708544. Its totient is φ = 66602700.

The previous prime is 66655613. The next prime is 66655661. The reversal of 66655621 is 12655666.

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: 12655666 = 2 ⋅6327833.

It is a cyclic number.

It is not a de Polignac number, because 66655621 - 2³ = 66655613 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 (66655661) 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, 24525 + ... + 27106.

It is an arithmetic number, because the mean of its divisors is an integer number (16677136).

Almost surely, 2^66655621 is an apocalyptic number.

It is an amenable number.

66655621 is a deficient number, since it is larger than the sum of its proper divisors (52923).

66655621 is a wasteful number, since it uses less digits than its factorization.

66655621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 52922.

The product of its digits is 64800, while the sum is 37.

The square root of 66655621 is about 8164.2893750773. The cubic root of 66655621 is about 405.4577378094.

It can be divided in two parts, 66655 and 621, that added together give a palindrome (67276).

The spelling of 66655621 in words is "sixty-six million, six hundred fifty-five thousand, six hundred twenty-one".