81285409 has 2 divisors, whose sum is σ = 81285410. Its totient is φ = 81285408.

The previous prime is 81285403. The next prime is 81285443. The reversal of 81285409 is 90458218.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 80013025 + 1272384 = 8945^2 + 1128^2 .

It is a cyclic number.

It is not a de Polignac number, because 81285409 - 2¹⁵ = 81252641 is a prime.

It is not a weakly prime, because it can be changed into another prime (81285403) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40642704 + 40642705.

It is an arithmetic number, because the mean of its divisors is an integer number (40642705).

Almost surely, 2^81285409 is an apocalyptic number.

It is an amenable number.

81285409 is a deficient number, since it is larger than the sum of its proper divisors (1).

81285409 is an equidigital number, since it uses as much as digits as its factorization.

81285409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 23040, while the sum is 37.

The square root of 81285409 is about 9015.8421126371. The cubic root of 81285409 is about 433.1824618106.

The spelling of 81285409 in words is "eighty-one million, two hundred eighty-five thousand, four hundred nine".