87921721 has 4 divisors (see below), whose sum is σ = 92549200. Its totient is φ = 83294244.

The previous prime is 87921677. The next prime is 87921749. The reversal of 87921721 is 12712978.

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 87921721 - 2¹¹ = 87919673 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (87921121) 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, 2313711 + ... + 2313748.

It is an arithmetic number, because the mean of its divisors is an integer number (23137300).

Almost surely, 2^87921721 is an apocalyptic number.

It is an amenable number.

87921721 is a deficient number, since it is larger than the sum of its proper divisors (4627479).

87921721 is a wasteful number, since it uses less digits than its factorization.

87921721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4627478.

The product of its digits is 14112, while the sum is 37.

The square root of 87921721 is about 9376.6583066677. The cubic root of 87921721 is about 444.6640919146.

The spelling of 87921721 in words is "eighty-seven million, nine hundred twenty-one thousand, seven hundred twenty-one".