71815781 has 2 divisors, whose sum is σ = 71815782. Its totient is φ = 71815780.

The previous prime is 71815753. The next prime is 71815817. The reversal of 71815781 is 18751817.

Together with next prime (71815817) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 62568100 + 9247681 = 7910^2 + 3041^2 .

It is a cyclic number.

It is not a de Polignac number, because 71815781 - 2²⁶ = 4706917 is a prime.

It is a super-2 number, since 2×71815781² = 10315012801279922, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (71815741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 35907890 + 35907891.

It is an arithmetic number, because the mean of its divisors is an integer number (35907891).

Almost surely, 2^71815781 is an apocalyptic number.

It is an amenable number.

71815781 is a deficient number, since it is larger than the sum of its proper divisors (1).

71815781 is an equidigital number, since it uses as much as digits as its factorization.

71815781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 15680, while the sum is 38.

The square root of 71815781 is about 8474.4192131379. The cubic root of 71815781 is about 415.6616551311.

The spelling of 71815781 in words is "seventy-one million, eight hundred fifteen thousand, seven hundred eighty-one".