66221621 has 2 divisors, whose sum is σ = 66221622. Its totient is φ = 66221620.

The previous prime is 66221569. The next prime is 66221627. The reversal of 66221621 is 12612266.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 52635025 + 13586596 = 7255^2 + 3686^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66221621 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66221627) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33110810 + 33110811.

It is an arithmetic number, because the mean of its divisors is an integer number (33110811).

Almost surely, 2^66221621 is an apocalyptic number.

It is an amenable number.

66221621 is a deficient number, since it is larger than the sum of its proper divisors (1).

66221621 is an equidigital number, since it uses as much as digits as its factorization.

66221621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1728, while the sum is 26.

The square root of 66221621 is about 8137.6668032059. Note that the first 3 decimals coincide. The cubic root of 66221621 is about 404.5758318859.

Adding to 66221621 its reverse (12612266), we get a palindrome (78833887).

The spelling of 66221621 in words is "sixty-six million, two hundred twenty-one thousand, six hundred twenty-one".