87191781 has 16 divisors (see below), whose sum is σ = 122196480. Its totient is φ = 55194480.

The previous prime is 87191761. The next prime is 87191791. The reversal of 87191781 is 18719178.

It is a happy number.

It is not a de Polignac number, because 87191781 - 2¹⁰ = 87190757 is a prime.

It is a super-3 number, since 3×87191781³ (a number of 25 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (87191701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5046 + ... + 14136.

It is an arithmetic number, because the mean of its divisors is an integer number (7637280).

Almost surely, 2^87191781 is an apocalyptic number.

It is an amenable number.

87191781 is a deficient number, since it is larger than the sum of its proper divisors (35004699).

87191781 is a wasteful number, since it uses less digits than its factorization.

87191781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9256.

The product of its digits is 28224, while the sum is 42.

The square root of 87191781 is about 9337.6539344741. The cubic root of 87191781 is about 443.4301135437.

The spelling of 87191781 in words is "eighty-seven million, one hundred ninety-one thousand, seven hundred eighty-one".