1608021661 has 4 divisors (see below), whose sum is σ = 1692654400. Its totient is φ = 1523388924.

The previous prime is 1608021659. The next prime is 1608021691. The reversal of 1608021661 is 1661208061.

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: 1661208061 = 5297 ⋅313613.

It is a cyclic number.

It is not a de Polignac number, because 1608021661 - 2¹ = 1608021659 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 (1608021631) 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, 42316341 + ... + 42316378.

It is an arithmetic number, because the mean of its divisors is an integer number (423163600).

Almost surely, 2^1608021661 is an apocalyptic number.

It is an amenable number.

1608021661 is a deficient number, since it is larger than the sum of its proper divisors (84632739).

1608021661 is an equidigital number, since it uses as much as digits as its factorization.

1608021661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 84632738.

The product of its (nonzero) digits is 3456, while the sum is 31.

The square root of 1608021661 is about 40100.1453987389. The cubic root of 1608021661 is about 1171.5584610815.

The spelling of 1608021661 in words is "one billion, six hundred eight million, twenty-one thousand, six hundred sixty-one".