1661645021 has 4 divisors (see below), whose sum is σ = 1685048544. Its totient is φ = 1638241500.

The previous prime is 1661644993. The next prime is 1661645047. The reversal of 1661645021 is 1205461661.

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: 1205461661 = 31531 ⋅38231.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1661645021 is a prime.

It is a super-2 number, since 2×1661645021² = 5522128351628180882, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661645071) 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, 11701655 + ... + 11701796.

It is an arithmetic number, because the mean of its divisors is an integer number (421262136).

Almost surely, 2^1661645021 is an apocalyptic number.

It is an amenable number.

1661645021 is a deficient number, since it is larger than the sum of its proper divisors (23403523).

1661645021 is an equidigital number, since it uses as much as digits as its factorization.

1661645021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23403522.

The product of its (nonzero) digits is 8640, while the sum is 32.

The square root of 1661645021 is about 40763.2803022524. The cubic root of 1661645021 is about 1184.4391397154.

The spelling of 1661645021 in words is "one billion, six hundred sixty-one million, six hundred forty-five thousand, twenty-one".