81998040609 has 15 divisors (see below), whose sum is σ = 122494750147. Its totient is φ = 54663642288.

The previous prime is 81998040547. The next prime is 81998040613. The reversal of 81998040609 is 90604089918.

The square root of 81998040609 is 286353.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 73557576225 + 8440464384 = 271215^2 + 91872^2 .

It is not a de Polignac number, because 81998040609 - 2²¹ = 81995943457 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81998040659) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 14 ways as a sum of consecutive naturals, for example, 2561269 + ... + 2593085.

Almost surely, 2^81998040609 is an apocalyptic number.

81998040609 is the 286353-rd square number.

81998040609 is the 143177-th centered octagonal number.

It is an amenable number.

81998040609 is a deficient number, since it is larger than the sum of its proper divisors (40496709538).

81998040609 is an frugal number, since it uses more digits than its factorization.

81998040609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 63646 (or 31820 counting only the distinct ones).

The product of its (nonzero) digits is 1119744, while the sum is 54.

The spelling of 81998040609 in words is "eighty-one billion, nine hundred ninety-eight million, forty thousand, six hundred nine".