1616217781 has 4 divisors (see below), whose sum is σ = 1623154572. Its totient is φ = 1609280992.

The previous prime is 1616217731. The next prime is 1616217791. The reversal of 1616217781 is 1877126161.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1877126161 = 73 ⋅25714057.

It can be written as a sum of positive squares in 2 ways, for example, as 277755556 + 1338462225 = 16666^2 + 36585^2 .

It is a cyclic number.

It is not a de Polignac number, because 1616217781 - 2⁹ = 1616217269 is a prime.

It is a super-2 number, since 2×1616217781² = 5224319831241127922, which 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 (1616217731) 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, 3468046 + ... + 3468511.

It is an arithmetic number, because the mean of its divisors is an integer number (405788643).

Almost surely, 2^1616217781 is an apocalyptic number.

It is an amenable number.

1616217781 is a deficient number, since it is larger than the sum of its proper divisors (6936791).

1616217781 is an equidigital number, since it uses as much as digits as its factorization.

1616217781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6936790.

The product of its digits is 28224, while the sum is 40.

The square root of 1616217781 is about 40202.2111456572. The cubic root of 1616217781 is about 1173.5455747598.

The spelling of 1616217781 in words is "one billion, six hundred sixteen million, two hundred seventeen thousand, seven hundred eighty-one".