66666621 has 16 divisors (see below), whose sum is σ = 105091200. Its totient is φ = 36781248.

The previous prime is 66666569. The next prime is 66666629. The reversal of 66666621 is 12666666.

It is not a de Polignac number, because 66666621 - 2⁶ = 66666557 is a prime.

It is a nialpdrome in base 10.

It is a self number, because there is not a number n which added to its sum of digits gives 66666621.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66666629) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 54126 + ... + 55343.

It is an arithmetic number, because the mean of its divisors is an integer number (6568200).

Almost surely, 2^66666621 is an apocalyptic number.

It is an amenable number.

66666621 is a deficient number, since it is larger than the sum of its proper divisors (38424579).

66666621 is a wasteful number, since it uses less digits than its factorization.

66666621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 109508.

The product of its digits is 93312, while the sum is 39.

The square root of 66666621 is about 8164.9630127760. The cubic root of 66666621 is about 405.4800404536.

It can be divided in two parts, 666666 and 21, that multiplied together give a triangular number (13999986 = T₅₂₉₁).

The spelling of 66666621 in words is "sixty-six million, six hundred sixty-six thousand, six hundred twenty-one".