81664061 has 2 divisors, whose sum is σ = 81664062. Its totient is φ = 81664060.

The previous prime is 81664031. The next prime is 81664067. The reversal of 81664061 is 16046618.

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., 41847961 + 39816100 = 6469^2 + 6310^2 .

It is a cyclic number.

It is not a de Polignac number, because 81664061 - 2¹⁸ = 81401917 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81664067) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40832030 + 40832031.

It is an arithmetic number, because the mean of its divisors is an integer number (40832031).

Almost surely, 2^81664061 is an apocalyptic number.

It is an amenable number.

81664061 is a deficient number, since it is larger than the sum of its proper divisors (1).

81664061 is an equidigital number, since it uses as much as digits as its factorization.

81664061 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6912, while the sum is 32.

The square root of 81664061 is about 9036.8169728063. The cubic root of 81664061 is about 433.8540516704.

The spelling of 81664061 in words is "eighty-one million, six hundred sixty-four thousand, sixty-one".