81312421 has 4 divisors (see below), whose sum is σ = 83510092. Its totient is φ = 79114752.

The previous prime is 81312367. The next prime is 81312461. The reversal of 81312421 is 12421318.

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 30404196 + 50908225 = 5514^2 + 7135^2 .

It is a cyclic number.

It is not a de Polignac number, because 81312421 - 2⁷ = 81312293 is a prime.

It is a super-2 number, since 2×81312421² = 13223419617762482, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81312392 and 81312401.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81312461) 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, 1098780 + ... + 1098853.

It is an arithmetic number, because the mean of its divisors is an integer number (20877523).

Almost surely, 2^81312421 is an apocalyptic number.

It is an amenable number.

81312421 is a deficient number, since it is larger than the sum of its proper divisors (2197671).

81312421 is a wasteful number, since it uses less digits than its factorization.

81312421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2197670.

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

The square root of 81312421 is about 9017.3400179876. The cubic root of 81312421 is about 433.2304401989.

Adding to 81312421 its reverse (12421318), we get a palindrome (93733739).

The spelling of 81312421 in words is "eighty-one million, three hundred twelve thousand, four hundred twenty-one".