1646651621 has 4 divisors (see below), whose sum is σ = 1647395244. Its totient is φ = 1645908000.

The previous prime is 1646651593. The next prime is 1646651651. The reversal of 1646651621 is 1261566461.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1261566461 = 149 ⋅8466889.

It can be written as a sum of positive squares in 2 ways, for example, as 602457025 + 1044194596 = 24545^2 + 32314^2 .

It is a cyclic number.

It is not a de Polignac number, because 1646651621 - 2²² = 1642457317 is a prime.

It is a super-2 number, since 2×1646651621² = 5422923121883855282, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a plaindrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1646651651) 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, 368480 + ... + 372921.

It is an arithmetic number, because the mean of its divisors is an integer number (411848811).

Almost surely, 2^1646651621 is an apocalyptic number.

It is an amenable number.

1646651621 is a deficient number, since it is larger than the sum of its proper divisors (743623).

1646651621 is an equidigital number, since it uses as much as digits as its factorization.

1646651621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 743622.

The product of its digits is 51840, while the sum is 38.

The square root of 1646651621 is about 40578.9553956235. The cubic root of 1646651621 is about 1180.8658829417.

The spelling of 1646651621 in words is "one billion, six hundred forty-six million, six hundred fifty-one thousand, six hundred twenty-one".