81218472761 has 4 divisors (see below), whose sum is σ = 81223393524. Its totient is φ = 81213552000.

The previous prime is 81218472677. The next prime is 81218472767. The reversal of 81218472761 is 16727481218.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 23531560000 + 57686912761 = 153400^2 + 240181^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81218472761 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81218472767) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2435540 + ... + 2468661.

It is an arithmetic number, because the mean of its divisors is an integer number (20305848381).

Almost surely, 2^81218472761 is an apocalyptic number.

It is an amenable number.

81218472761 is a deficient number, since it is larger than the sum of its proper divisors (4920763).

81218472761 is a wasteful number, since it uses less digits than its factorization.

81218472761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4920762.

The product of its digits is 301056, while the sum is 47.

The spelling of 81218472761 in words is "eighty-one billion, two hundred eighteen million, four hundred seventy-two thousand, seven hundred sixty-one".