15781131815661 has 8 divisors (see below), whose sum is σ = 23379454541760. Its totient is φ = 10520754543756.

The previous prime is 15781131815623. The next prime is 15781131815773. The reversal of 15781131815661 is 16651813118751.

15781131815661 is a `hidden beast` number, since 1 + 5 + 78 + 1 + 1 + 3 + 1 + 8 + 1 + 566 + 1 = 666.

15781131815661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 15781131815661 - 2⁹ = 15781131815149 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 15781131815598 and 15781131815607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15781131815461) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 292243181745 + ... + 292243181798.

It is an arithmetic number, because the mean of its divisors is an integer number (2922431817720).

Almost surely, 2^{15781131815661} is an apocalyptic number.

It is an amenable number.

15781131815661 is a deficient number, since it is larger than the sum of its proper divisors (7598322726099).

15781131815661 is an equidigital number, since it uses as much as digits as its factorization.

15781131815661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 584486363552 (or 584486363546 counting only the distinct ones).

The product of its digits is 1209600, while the sum is 54.

The spelling of 15781131815661 in words is "fifteen trillion, seven hundred eighty-one billion, one hundred thirty-one million, eight hundred fifteen thousand, six hundred sixty-one".