81197921 has 4 divisors (see below), whose sum is σ = 92797632. Its totient is φ = 69598212.

The previous prime is 81197891. The next prime is 81197927. The reversal of 81197921 is 12979118.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12979118 = 2 ⋅6489559.

It is a cyclic number.

It is not a de Polignac number, because 81197921 - 2¹⁴ = 81181537 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81197927) 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, 5799845 + ... + 5799858.

It is an arithmetic number, because the mean of its divisors is an integer number (23199408).

Almost surely, 2^81197921 is an apocalyptic number.

It is an amenable number.

81197921 is a deficient number, since it is larger than the sum of its proper divisors (11599711).

81197921 is a wasteful number, since it uses less digits than its factorization.

81197921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11599710.

The product of its digits is 9072, while the sum is 38.

The square root of 81197921 is about 9010.9889024457. The cubic root of 81197921 is about 433.0269936787.

The spelling of 81197921 in words is "eighty-one million, one hundred ninety-seven thousand, nine hundred twenty-one".