661620561 has 8 divisors (see below), whose sum is σ = 1008183744. Its totient is φ = 378068880.

The previous prime is 661620541. The next prime is 661620563. The reversal of 661620561 is 165026166.

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

It is a de Polignac number, because none of the positive numbers 2^k-661620561 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661620563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15752850 + ... + 15752891.

It is an arithmetic number, because the mean of its divisors is an integer number (126022968).

Almost surely, 2^661620561 is an apocalyptic number.

It is an amenable number.

661620561 is a deficient number, since it is larger than the sum of its proper divisors (346563183).

661620561 is a wasteful number, since it uses less digits than its factorization.

661620561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31505751.

The product of its (nonzero) digits is 12960, while the sum is 33.

The square root of 661620561 is about 25721.9859458791. The cubic root of 661620561 is about 871.3707905316.

The spelling of 661620561 in words is "six hundred sixty-one million, six hundred twenty thousand, five hundred sixty-one".