81421421 has 2 divisors, whose sum is σ = 81421422. Its totient is φ = 81421420.

The previous prime is 81421411. The next prime is 81421463. The reversal of 81421421 is 12412418.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 72505225 + 8916196 = 8515^2 + 2986^2 .

It is a cyclic number.

It is not a de Polignac number, because 81421421 - 2¹⁰ = 81420397 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81421411) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40710710 + 40710711.

It is an arithmetic number, because the mean of its divisors is an integer number (40710711).

Almost surely, 2^81421421 is an apocalyptic number.

It is an amenable number.

81421421 is a deficient number, since it is larger than the sum of its proper divisors (1).

81421421 is an equidigital number, since it uses as much as digits as its factorization.

81421421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 512, while the sum is 23.

The square root of 81421421 is about 9023.3819048071. The cubic root of 81421421 is about 433.4239368077.

Adding to 81421421 its reverse (12412418), we get a palindrome (93833839).

The spelling of 81421421 in words is "eighty-one million, four hundred twenty-one thousand, four hundred twenty-one".