187721 has 2 divisors, whose sum is σ = 187722. Its totient is φ = 187720.

The previous prime is 187711. The next prime is 187751. The reversal of 187721 is 127781.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 132496 + 55225 = 364^2 + 235^2 .

It is an emirp because it is prime and its reverse (127781) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-187721 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is an Ulam number.

It is a Curzon number.

It is equal to p₁₆₉₈₂ and since 187721 and 16982 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 187721.

It is not a weakly prime, because it can be changed into another prime (187711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 93860 + 93861.

It is an arithmetic number, because the mean of its divisors is an integer number (93861).

2¹⁸⁷⁷²¹ is an apocalyptic number.

It is an amenable number.

187721 is a deficient number, since it is larger than the sum of its proper divisors (1).

187721 is an equidigital number, since it uses as much as digits as its factorization.

187721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 784, while the sum is 26.

The square root of 187721 is about 433.2678155598. The cubic root of 187721 is about 57.2581905738.

The spelling of 187721 in words is "one hundred eighty-seven thousand, seven hundred twenty-one".