81291987 has 24 divisors (see below), whose sum is σ = 134956640. Its totient is φ = 46189440.

The previous prime is 81291967. The next prime is 81291989. The reversal of 81291987 is 78919218.

It is not a de Polignac number, because 81291987 - 2¹¹ = 81289939 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81291989) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7839 + ... + 14967.

Almost surely, 2^81291987 is an apocalyptic number.

81291987 is a deficient number, since it is larger than the sum of its proper divisors (53664653).

81291987 is a wasteful number, since it uses less digits than its factorization.

81291987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7323 (or 7320 counting only the distinct ones).

The product of its digits is 72576, while the sum is 45.

The square root of 81291987 is about 9016.2069075637. The cubic root of 81291987 is about 433.1941465537.

The spelling of 81291987 in words is "eighty-one million, two hundred ninety-one thousand, nine hundred eighty-seven".