81541778489 has 2 divisors, whose sum is σ = 81541778490. Its totient is φ = 81541778488.

The previous prime is 81541778473. The next prime is 81541778497. The reversal of 81541778489 is 98487714518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81518815225 + 22963264 = 285515^2 + 4792^2 .

It is a cyclic number.

It is not a de Polignac number, because 81541778489 - 2⁴ = 81541778473 is a prime.

It is not a weakly prime, because it can be changed into another prime (81541778449) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40770889244 + 40770889245.

It is an arithmetic number, because the mean of its divisors is an integer number (40770889245).

Almost surely, 2^81541778489 is an apocalyptic number.

It is an amenable number.

81541778489 is a deficient number, since it is larger than the sum of its proper divisors (1).

81541778489 is an equidigital number, since it uses as much as digits as its factorization.

81541778489 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18063360, while the sum is 62.

The spelling of 81541778489 in words is "eighty-one billion, five hundred forty-one million, seven hundred seventy-eight thousand, four hundred eighty-nine".