81386521 has 2 divisors, whose sum is σ = 81386522. Its totient is φ = 81386520.

The previous prime is 81386483. The next prime is 81386533. The reversal of 81386521 is 12568318.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 56025225 + 25361296 = 7485^2 + 5036^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81386521 is a prime.

It is not a weakly prime, because it can be changed into another prime (81386321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40693260 + 40693261.

It is an arithmetic number, because the mean of its divisors is an integer number (40693261).

Almost surely, 2^81386521 is an apocalyptic number.

It is an amenable number.

81386521 is a deficient number, since it is larger than the sum of its proper divisors (1).

81386521 is an equidigital number, since it uses as much as digits as its factorization.

81386521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 11520, while the sum is 34.

The square root of 81386521 is about 9021.4478328038. The cubic root of 81386521 is about 433.3620011935.

The spelling of 81386521 in words is "eighty-one million, three hundred eighty-six thousand, five hundred twenty-one".