1667651221 has 4 divisors (see below), whose sum is σ = 1667739744. Its totient is φ = 1667562700.

The previous prime is 1667651213. The next prime is 1667651233. The reversal of 1667651221 is 1221567661.

It is a happy number.

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 a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 1221567661 = 127 ⋅9618643.

It is a cyclic number.

It is not a de Polignac number, because 1667651221 - 2³ = 1667651213 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 (1667651281) 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, 3475 + ... + 57856.

It is an arithmetic number, because the mean of its divisors is an integer number (416934936).

Almost surely, 2^1667651221 is an apocalyptic number.

It is an amenable number.

1667651221 is a deficient number, since it is larger than the sum of its proper divisors (88523).

1667651221 is an equidigital number, since it uses as much as digits as its factorization.

1667651221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 88522.

The product of its digits is 30240, while the sum is 37.

The square root of 1667651221 is about 40836.8855448111. The cubic root of 1667651221 is about 1185.8645191880.

The spelling of 1667651221 in words is "one billion, six hundred sixty-seven million, six hundred fifty-one thousand, two hundred twenty-one".