187999921 has 2 divisors, whose sum is σ = 187999922. Its totient is φ = 187999920.

The previous prime is 187999919. The next prime is 187999961. The reversal of 187999921 is 129999781.

187999921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 185640625 + 2359296 = 13625^2 + 1536^2 .

It is an emirp because it is prime and its reverse (129999781) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 187999921 - 2¹ = 187999919 is a prime.

Together with 187999919, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (187999961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 93999960 + 93999961.

It is an arithmetic number, because the mean of its divisors is an integer number (93999961).

Almost surely, 2^187999921 is an apocalyptic number.

It is an amenable number.

187999921 is a deficient number, since it is larger than the sum of its proper divisors (1).

187999921 is an equidigital number, since it uses as much as digits as its factorization.

187999921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 734832, while the sum is 55.

The square root of 187999921 is about 13711.3063199682. The cubic root of 187999921 is about 572.8653513564.

The spelling of 187999921 in words is "one hundred eighty-seven million, nine hundred ninety-nine thousand, nine hundred twenty-one".