661578861 has 4 divisors (see below), whose sum is σ = 882105152. Its totient is φ = 441052572.

The previous prime is 661578847. The next prime is 661578881. The reversal of 661578861 is 168875166.

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.

It is not a de Polignac number, because 661578861 - 2¹¹ = 661576813 is a prime.

It is a super-3 number, since 3×661578861³ (a number of 27 digits) contains 333 as substring.

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 661578861.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661578821) 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, 110263141 + ... + 110263146.

It is an arithmetic number, because the mean of its divisors is an integer number (220526288).

Almost surely, 2^661578861 is an apocalyptic number.

It is an amenable number.

661578861 is a deficient number, since it is larger than the sum of its proper divisors (220526291).

661578861 is a wasteful number, since it uses less digits than its factorization.

661578861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 220526290.

The product of its digits is 483840, while the sum is 48.

The square root of 661578861 is about 25721.1753425072. The cubic root of 661578861 is about 871.3524835001.

The spelling of 661578861 in words is "six hundred sixty-one million, five hundred seventy-eight thousand, eight hundred sixty-one".