81554721261 has 16 divisors (see below), whose sum is σ = 118140542016. Its totient is φ = 49743380736.

The previous prime is 81554721239. The next prime is 81554721271. The reversal of 81554721261 is 16212745518.

It is a happy number.

It is not a de Polignac number, because 81554721261 - 2¹⁷ = 81554590189 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81554721271) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9248455 + ... + 9257268.

It is an arithmetic number, because the mean of its divisors is an integer number (7383783876).

Almost surely, 2^81554721261 is an apocalyptic number.

It is an amenable number.

81554721261 is a deficient number, since it is larger than the sum of its proper divisors (36585820755).

81554721261 is a wasteful number, since it uses less digits than its factorization.

81554721261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18505852.

The product of its digits is 134400, while the sum is 42.

The spelling of 81554721261 in words is "eighty-one billion, five hundred fifty-four million, seven hundred twenty-one thousand, two hundred sixty-one".