661804561 has 32 divisors (see below), whose sum is σ = 779950080. Its totient is φ = 555206400.

The previous prime is 661804547. The next prime is 661804573. The reversal of 661804561 is 165408166.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-661804561 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 661804561.

It is not an unprimeable number, because it can be changed into a prime (661804531) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1528201 + ... + 1528633.

It is an arithmetic number, because the mean of its divisors is an integer number (24373440).

Almost surely, 2^661804561 is an apocalyptic number.

It is an amenable number.

661804561 is a deficient number, since it is larger than the sum of its proper divisors (118145519).

661804561 is a wasteful number, since it uses less digits than its factorization.

661804561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 637.

The product of its (nonzero) digits is 34560, while the sum is 37.

The square root of 661804561 is about 25725.5624039592. The cubic root of 661804561 is about 871.4515605752.

The spelling of 661804561 in words is "six hundred sixty-one million, eight hundred four thousand, five hundred sixty-one".