81366421 has 2 divisors, whose sum is σ = 81366422. Its totient is φ = 81366420.

The previous prime is 81366409. The next prime is 81366443. The reversal of 81366421 is 12466318.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 45832900 + 35533521 = 6770^2 + 5961^2 .

It is a cyclic number.

It is not a de Polignac number, because 81366421 - 2¹¹ = 81364373 is a prime.

It is a Chen prime.

It is equal to p_4744624 and since 81366421 and 4744624 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81366491) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40683210 + 40683211.

It is an arithmetic number, because the mean of its divisors is an integer number (40683211).

Almost surely, 2^81366421 is an apocalyptic number.

It is an amenable number.

81366421 is a deficient number, since it is larger than the sum of its proper divisors (1).

81366421 is an equidigital number, since it uses as much as digits as its factorization.

81366421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6912, while the sum is 31.

The square root of 81366421 is about 9020.3337521402. Note that the first 3 decimals coincide. The cubic root of 81366421 is about 433.3263225033.

The spelling of 81366421 in words is "eighty-one million, three hundred sixty-six thousand, four hundred twenty-one".