187721561 has 4 divisors (see below), whose sum is σ = 195883392. Its totient is φ = 179559732.

The previous prime is 187721507. The next prime is 187721563. The reversal of 187721561 is 165127781.

It is a happy number.

187721561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 a cyclic number.

It is not a de Polignac number, because 187721561 - 2¹⁰ = 187720537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (187721563) 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, 4080881 + ... + 4080926.

It is an arithmetic number, because the mean of its divisors is an integer number (48970848).

Almost surely, 2^187721561 is an apocalyptic number.

It is an amenable number.

187721561 is a deficient number, since it is larger than the sum of its proper divisors (8161831).

187721561 is an equidigital number, since it uses as much as digits as its factorization.

187721561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8161830.

The product of its digits is 23520, while the sum is 38.

The square root of 187721561 is about 13701.1518128951. The cubic root of 187721561 is about 572.5824761201.

The spelling of 187721561 in words is "one hundred eighty-seven million, seven hundred twenty-one thousand, five hundred sixty-one".