81321637 has 2 divisors, whose sum is σ = 81321638. Its totient is φ = 81321636.

The previous prime is 81321619. The next prime is 81321641. The reversal of 81321637 is 73612318.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 75794436 + 5527201 = 8706^2 + 2351^2 .

It is a cyclic number.

It is not a de Polignac number, because 81321637 - 2⁷ = 81321509 is a prime.

It is a super-2 number, since 2×81321637² = 13226417288719538, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81321599 and 81321608.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81321697) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40660818 + 40660819.

It is an arithmetic number, because the mean of its divisors is an integer number (40660819).

Almost surely, 2^81321637 is an apocalyptic number.

It is an amenable number.

81321637 is a deficient number, since it is larger than the sum of its proper divisors (1).

81321637 is an equidigital number, since it uses as much as digits as its factorization.

81321637 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6048, while the sum is 31.

The square root of 81321637 is about 9017.8510189512. The cubic root of 81321637 is about 433.2468071158.

The spelling of 81321637 in words is "eighty-one million, three hundred twenty-one thousand, six hundred thirty-seven".