81213252921 has 6 divisors (see below), whose sum is σ = 117308032010. Its totient is φ = 54142168608.

The previous prime is 81213252919. The next prime is 81213252949. The reversal of 81213252921 is 12925231218.

81213252921 is a `hidden beast` number, since 8 + 121 + 3 + 2 + 529 + 2 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 49390617600 + 31822635321 = 222240^2 + 178389^2 .

It is not a de Polignac number, because 81213252921 - 2¹ = 81213252919 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81213252821) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4511847376 + ... + 4511847393.

Almost surely, 2^81213252921 is an apocalyptic number.

It is an amenable number.

81213252921 is a deficient number, since it is larger than the sum of its proper divisors (36094779089).

81213252921 is a wasteful number, since it uses less digits than its factorization.

81213252921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9023694775 (or 9023694772 counting only the distinct ones).

The product of its digits is 17280, while the sum is 36.

The spelling of 81213252921 in words is "eighty-one billion, two hundred thirteen million, two hundred fifty-two thousand, nine hundred twenty-one".