81504781 has 2 divisors, whose sum is σ = 81504782. Its totient is φ = 81504780.

The previous prime is 81504767. The next prime is 81504791. The reversal of 81504781 is 18740518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 67322025 + 14182756 = 8205^2 + 3766^2 .

It is a cyclic number.

It is not a de Polignac number, because 81504781 - 2⁷ = 81504653 is a prime.

It is a super-2 number, since 2×81504781² = 13286058651715922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81504701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40752390 + 40752391.

It is an arithmetic number, because the mean of its divisors is an integer number (40752391).

Almost surely, 2^81504781 is an apocalyptic number.

It is an amenable number.

81504781 is a deficient number, since it is larger than the sum of its proper divisors (1).

81504781 is an equidigital number, since it uses as much as digits as its factorization.

81504781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8960, while the sum is 34.

The square root of 81504781 is about 9027.9998338502. Note that the first 3 decimals coincide. The cubic root of 81504781 is about 433.5718008291.

The spelling of 81504781 in words is "eighty-one million, five hundred four thousand, seven hundred eighty-one".