81212501 has 4 divisors (see below), whose sum is σ = 81238572. Its totient is φ = 81186432.

The previous prime is 81212491. The next prime is 81212503. The reversal of 81212501 is 10521218.

It is a happy number.

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 3243601 + 77968900 = 1801^2 + 8830^2 .

It is a cyclic number.

It is not a de Polignac number, because 81212501 - 2¹⁴ = 81196117 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81212503) 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, 7610 + ... + 14843.

It is an arithmetic number, because the mean of its divisors is an integer number (20309643).

Almost surely, 2^81212501 is an apocalyptic number.

It is an amenable number.

81212501 is a deficient number, since it is larger than the sum of its proper divisors (26071).

81212501 is a wasteful number, since it uses less digits than its factorization.

81212501 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26070.

The product of its (nonzero) digits is 160, while the sum is 20.

The square root of 81212501 is about 9011.7978783370. The cubic root of 81212501 is about 433.0529104166.

Adding to 81212501 its reverse (10521218), we get a palindrome (91733719).

The spelling of 81212501 in words is "eighty-one million, two hundred twelve thousand, five hundred one".