81640261 has 2 divisors, whose sum is σ = 81640262. Its totient is φ = 81640260.

The previous prime is 81640243. The next prime is 81640291. The reversal of 81640261 is 16204618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 80892036 + 748225 = 8994^2 + 865^2 .

It is a cyclic number.

It is not a de Polignac number, because 81640261 - 2⁹ = 81639749 is a prime.

It is a super-2 number, since 2×81640261² = 13330264432296242, which contains 22 as substring.

It is a Chen prime.

It is the 9036-th Hogben number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81640201) by changing a digit.

It is a nontrivial repunit in base 9035.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40820130 + 40820131.

It is an arithmetic number, because the mean of its divisors is an integer number (40820131).

Almost surely, 2^81640261 is an apocalyptic number.

It is an amenable number.

81640261 is a deficient number, since it is larger than the sum of its proper divisors (1).

81640261 is an equidigital number, since it uses as much as digits as its factorization.

81640261 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2304, while the sum is 28.

The square root of 81640261 is about 9035.5000415030. The cubic root of 81640261 is about 433.8119004084.

Adding to 81640261 its reverse (16204618), we get a palindrome (97844879).

The spelling of 81640261 in words is "eighty-one million, six hundred forty thousand, two hundred sixty-one".