15661821317 has 4 divisors (see below), whose sum is σ = 15678864480. Its totient is φ = 15644778156.

The previous prime is 15661821313. The next prime is 15661821347. The reversal of 15661821317 is 71312816651.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 71312816651 = 37 ⋅1927373423.

It is a cyclic number.

It is not a de Polignac number, because 15661821317 - 2² = 15661821313 is a prime.

It is a super-2 number, since 2×15661821317² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15661821313) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8520203 + ... + 8522040.

It is an arithmetic number, because the mean of its divisors is an integer number (3919716120).

Almost surely, 2^15661821317 is an apocalyptic number.

It is an amenable number.

15661821317 is a deficient number, since it is larger than the sum of its proper divisors (17043163).

15661821317 is an equidigital number, since it uses as much as digits as its factorization.

15661821317 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17043162.

The product of its digits is 60480, while the sum is 41.

The spelling of 15661821317 in words is "fifteen billion, six hundred sixty-one million, eight hundred twenty-one thousand, three hundred seventeen".