81213973 has 2 divisors, whose sum is σ = 81213974. Its totient is φ = 81213972.

The previous prime is 81213959. The next prime is 81214009. The reversal of 81213973 is 37931218.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 70442449 + 10771524 = 8393^2 + 3282^2 .

It is a cyclic number.

It is not a de Polignac number, because 81213973 - 2²⁵ = 47659541 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81213953) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40606986 + 40606987.

It is an arithmetic number, because the mean of its divisors is an integer number (40606987).

Almost surely, 2^81213973 is an apocalyptic number.

It is an amenable number.

81213973 is a deficient number, since it is larger than the sum of its proper divisors (1).

81213973 is an equidigital number, since it uses as much as digits as its factorization.

81213973 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9072, while the sum is 34.

The square root of 81213973 is about 9011.8795486846. The cubic root of 81213973 is about 433.0555268037.

The spelling of 81213973 in words is "eighty-one million, two hundred thirteen thousand, nine hundred seventy-three".