81681961 has 2 divisors, whose sum is σ = 81681962. Its totient is φ = 81681960.

The previous prime is 81681953. The next prime is 81682031. The reversal of 81681961 is 16918618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 48734361 + 32947600 = 6981^2 + 5740^2 .

It is a cyclic number.

It is not a de Polignac number, because 81681961 - 2³ = 81681953 is a prime.

It is equal to p_4761976 and since 81681961 and 4761976 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (81681461) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40840980 + 40840981.

It is an arithmetic number, because the mean of its divisors is an integer number (40840981).

Almost surely, 2^81681961 is an apocalyptic number.

It is an amenable number.

81681961 is a deficient number, since it is larger than the sum of its proper divisors (1).

81681961 is an equidigital number, since it uses as much as digits as its factorization.

81681961 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20736, while the sum is 40.

The square root of 81681961 is about 9037.8073115109. The cubic root of 81681961 is about 433.8857482744.

The spelling of 81681961 in words is "eighty-one million, six hundred eighty-one thousand, nine hundred sixty-one".