1987195721 has 8 divisors (see below), whose sum is σ = 2280829824. Its totient is φ = 1695998880.

The previous prime is 1987195687. The next prime is 1987195729. The reversal of 1987195721 is 1275917891.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1987195721 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1987195721.

It is not an unprimeable number, because it can be changed into a prime (1987195729) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 607565 + ... + 610826.

It is an arithmetic number, because the mean of its divisors is an integer number (285103728).

Almost surely, 2^1987195721 is an apocalyptic number.

It is an amenable number.

1987195721 is a deficient number, since it is larger than the sum of its proper divisors (293634103).

1987195721 is a wasteful number, since it uses less digits than its factorization.

1987195721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1218631.

The product of its digits is 317520, while the sum is 50.

The square root of 1987195721 is about 44577.9734958870. The cubic root of 1987195721 is about 1257.2265614173.

The spelling of 1987195721 in words is "one billion, nine hundred eighty-seven million, one hundred ninety-five thousand, seven hundred twenty-one".