81026511645581 has 4 divisors (see below), whose sum is σ = 81783768763872. Its totient is φ = 80269254527292.

The previous prime is 81026511645553. The next prime is 81026511645593. The reversal of 81026511645581 is 18554611562018.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81026511645581 - 2¹⁴ = 81026511629197 is a prime.

It is a super-2 number, since 2×81026511645581² (a number of 29 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81026511045581) 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, 378628558985 + ... + 378628559198.

It is an arithmetic number, because the mean of its divisors is an integer number (20445942190968).

Almost surely, 2^{81026511645581} is an apocalyptic number.

It is an amenable number.

81026511645581 is a deficient number, since it is larger than the sum of its proper divisors (757257118291).

81026511645581 is a wasteful number, since it uses less digits than its factorization.

81026511645581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 757257118290.

The product of its (nonzero) digits is 2304000, while the sum is 53.

The spelling of 81026511645581 in words is "eighty-one trillion, twenty-six billion, five hundred eleven million, six hundred forty-five thousand, five hundred eighty-one".