87991861 has 2 divisors, whose sum is σ = 87991862. Its totient is φ = 87991860.

The previous prime is 87991817. The next prime is 87991873. The reversal of 87991861 is 16819978.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 59582961 + 28408900 = 7719^2 + 5330^2 .

It is a cyclic number.

It is not a de Polignac number, because 87991861 - 2¹⁹ = 87467573 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (87991811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 43995930 + 43995931.

It is an arithmetic number, because the mean of its divisors is an integer number (43995931).

Almost surely, 2^87991861 is an apocalyptic number.

It is an amenable number.

87991861 is a deficient number, since it is larger than the sum of its proper divisors (1).

87991861 is an equidigital number, since it uses as much as digits as its factorization.

87991861 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 217728, while the sum is 49.

The square root of 87991861 is about 9380.3976994582. The cubic root of 87991861 is about 444.7823048320.

The spelling of 87991861 in words is "eighty-seven million, nine hundred ninety-one thousand, eight hundred sixty-one".