1661603521 has 8 divisors (see below), whose sum is σ = 1677981800. Its totient is φ = 1645246080.

The previous prime is 1661603491. The next prime is 1661603527. The reversal of 1661603521 is 1253061661.

It can be written as a sum of positive squares in 4 ways, for example, as 788991921 + 872611600 = 28089^2 + 29540^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1661603521 - 2¹³ = 1661595329 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1661603527) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 190741 + ... + 199261.

It is an arithmetic number, because the mean of its divisors is an integer number (209747725).

Almost surely, 2^1661603521 is an apocalyptic number.

It is an amenable number.

1661603521 is a deficient number, since it is larger than the sum of its proper divisors (16378279).

1661603521 is a wasteful number, since it uses less digits than its factorization.

1661603521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10419.

The product of its (nonzero) digits is 6480, while the sum is 31.

The square root of 1661603521 is about 40762.7712625135. The cubic root of 1661603521 is about 1184.4292790787.

The spelling of 1661603521 in words is "one billion, six hundred sixty-one million, six hundred three thousand, five hundred twenty-one".