81302521 has 2 divisors, whose sum is σ = 81302522. Its totient is φ = 81302520.

The previous prime is 81302497. The next prime is 81302581. The reversal of 81302521 is 12520318.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 78943225 + 2359296 = 8885^2 + 1536^2 .

It is a cyclic number.

It is not a de Polignac number, because 81302521 - 2¹⁵ = 81269753 is a prime.

It is a super-2 number, since 2×81302521² = 13220199841910882, which contains 22 as substring.

It is a Chen prime.

It is equal to p_4741123 and since 81302521 and 4741123 have the same sum of digits, it is a Honaker prime.

It is a junction number, because it is equal to n+sod(n) for n = 81302492 and 81302501.

It is not a weakly prime, because it can be changed into another prime (81302581) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40651260 + 40651261.

It is an arithmetic number, because the mean of its divisors is an integer number (40651261).

Almost surely, 2^81302521 is an apocalyptic number.

It is an amenable number.

81302521 is a deficient number, since it is larger than the sum of its proper divisors (1).

81302521 is an equidigital number, since it uses as much as digits as its factorization.

81302521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 480, while the sum is 22.

The square root of 81302521 is about 9016.7910589078. The cubic root of 81302521 is about 433.2128571721.

Adding to 81302521 its reverse (12520318), we get a palindrome (93822839).

The spelling of 81302521 in words is "eighty-one million, three hundred two thousand, five hundred twenty-one".