81919009013 has 2 divisors, whose sum is σ = 81919009014. Its totient is φ = 81919009012.

The previous prime is 81919008947. The next prime is 81919009021. The reversal of 81919009013 is 31090091918.

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., 54879153169 + 27039855844 = 234263^2 + 164438^2 .

It is a cyclic number.

It is not a de Polignac number, because 81919009013 - 2¹⁸ = 81918746869 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81919009213) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40959504506 + 40959504507.

It is an arithmetic number, because the mean of its divisors is an integer number (40959504507).

Almost surely, 2^81919009013 is an apocalyptic number.

It is an amenable number.

81919009013 is a deficient number, since it is larger than the sum of its proper divisors (1).

81919009013 is an equidigital number, since it uses as much as digits as its factorization.

81919009013 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 17496, while the sum is 41.

The spelling of 81919009013 in words is "eighty-one billion, nine hundred nineteen million, nine thousand, thirteen".