81003781 has 2 divisors, whose sum is σ = 81003782. Its totient is φ = 81003780.

The previous prime is 81003763. The next prime is 81003803. The reversal of 81003781 is 18730018.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 67387681 + 13616100 = 8209^2 + 3690^2 .

It is a cyclic number.

It is not a de Polignac number, because 81003781 - 2⁷ = 81003653 is a prime.

It is a super-2 number, since 2×81003781² = 13123225072591922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81003721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40501890 + 40501891.

It is an arithmetic number, because the mean of its divisors is an integer number (40501891).

Almost surely, 2^81003781 is an apocalyptic number.

It is an amenable number.

81003781 is a deficient number, since it is larger than the sum of its proper divisors (1).

81003781 is an equidigital number, since it uses as much as digits as its factorization.

81003781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1344, while the sum is 28.

The square root of 81003781 is about 9000.2100531043. The cubic root of 81003781 is about 432.6816032660.

Adding to 81003781 its reverse (18730018), we get a palindrome (99733799).

It can be divided in two parts, 8100 and 3781, that added together give a square (11881 = 109²).

The spelling of 81003781 in words is "eighty-one million, three thousand, seven hundred eighty-one".