81437821 has 2 divisors, whose sum is σ = 81437822. Its totient is φ = 81437820.

The previous prime is 81437809. The next prime is 81437827. The reversal of 81437821 is 12873418.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 70744921 + 10692900 = 8411^2 + 3270^2 .

It is a cyclic number.

It is not a de Polignac number, because 81437821 - 2⁷ = 81437693 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81437827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40718910 + 40718911.

It is an arithmetic number, because the mean of its divisors is an integer number (40718911).

Almost surely, 2^81437821 is an apocalyptic number.

It is an amenable number.

81437821 is a deficient number, since it is larger than the sum of its proper divisors (1).

81437821 is an equidigital number, since it uses as much as digits as its factorization.

81437821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10752, while the sum is 34.

The square root of 81437821 is about 9024.2906092390. The cubic root of 81437821 is about 433.4530351100.

The spelling of 81437821 in words is "eighty-one million, four hundred thirty-seven thousand, eight hundred twenty-one".