81020641 has 4 divisors (see below), whose sum is σ = 87253012. Its totient is φ = 74788272.

The previous prime is 81020593. The next prime is 81020647. The reversal of 81020641 is 14602018.

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 52707600 + 28313041 = 7260^2 + 5321^2 .

It is not a de Polignac number, because 81020641 - 2⁹ = 81020129 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81020647) 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, 3116166 + ... + 3116191.

It is an arithmetic number, because the mean of its divisors is an integer number (21813253).

Almost surely, 2^81020641 is an apocalyptic number.

It is an amenable number.

81020641 is a deficient number, since it is larger than the sum of its proper divisors (6232371).

81020641 is a wasteful number, since it uses less digits than its factorization.

81020641 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6232370.

The product of its (nonzero) digits is 384, while the sum is 22.

The square root of 81020641 is about 9001.1466491775. The cubic root of 81020641 is about 432.7116204071.

Adding to 81020641 its reverse (14602018), we get a palindrome (95622659).

The spelling of 81020641 in words is "eighty-one million, twenty thousand, six hundred forty-one".