81502991 has 4 divisors (see below), whose sum is σ = 81646800. Its totient is φ = 81359184.

The previous prime is 81502987. The next prime is 81502997. The reversal of 81502991 is 19920518.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19920518 = 2 ⋅9960259.

It is a cyclic number.

It is not a de Polignac number, because 81502991 - 2² = 81502987 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81502997) 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, 71051 + ... + 72188.

It is an arithmetic number, because the mean of its divisors is an integer number (20411700).

Almost surely, 2^81502991 is an apocalyptic number.

81502991 is a deficient number, since it is larger than the sum of its proper divisors (143809).

81502991 is a wasteful number, since it uses less digits than its factorization.

81502991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 143808.

The product of its (nonzero) digits is 6480, while the sum is 35.

The square root of 81502991 is about 9027.9006972828. The cubic root of 81502991 is about 433.5686267854.

The spelling of 81502991 in words is "eighty-one million, five hundred two thousand, nine hundred ninety-one".