81542581 has 2 divisors, whose sum is σ = 81542582. Its totient is φ = 81542580.

The previous prime is 81542507. The next prime is 81542599. The reversal of 81542581 is 18524518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81540900 + 1681 = 9030^2 + 41^2 .

It is a cyclic number.

It is not a de Polignac number, because 81542581 - 2¹⁹ = 81018293 is a prime.

It is a super-2 number, since 2×81542581² = 13298385032283122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81542381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40771290 + 40771291.

It is an arithmetic number, because the mean of its divisors is an integer number (40771291).

Almost surely, 2^81542581 is an apocalyptic number.

It is an amenable number.

81542581 is a deficient number, since it is larger than the sum of its proper divisors (1).

81542581 is an equidigital number, since it uses as much as digits as its factorization.

81542581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12800, while the sum is 34.

The square root of 81542581 is about 9030.0930781471. The cubic root of 81542581 is about 433.6388172704.

The spelling of 81542581 in words is "eighty-one million, five hundred forty-two thousand, five hundred eighty-one".