87191821 has 2 divisors, whose sum is σ = 87191822. Its totient is φ = 87191820.

The previous prime is 87191807. The next prime is 87191833. The reversal of 87191821 is 12819178.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 86955625 + 236196 = 9325^2 + 486^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-87191821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (87191921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 43595910 + 43595911.

It is an arithmetic number, because the mean of its divisors is an integer number (43595911).

Almost surely, 2^87191821 is an apocalyptic number.

It is an amenable number.

87191821 is a deficient number, since it is larger than the sum of its proper divisors (1).

87191821 is an equidigital number, since it uses as much as digits as its factorization.

87191821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8064, while the sum is 37.

The square root of 87191821 is about 9337.6560763395. The cubic root of 87191821 is about 443.4301813529.

The spelling of 87191821 in words is "eighty-seven million, one hundred ninety-one thousand, eight hundred twenty-one".