1361721991 has 4 divisors (see below), whose sum is σ = 1556253712. Its totient is φ = 1167190272.

The previous prime is 1361721961. The next prime is 1361721997. The reversal of 1361721991 is 1991271631.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1991271631 = 29 ⋅68664539.

It is a cyclic number.

It is not a de Polignac number, because 1361721991 - 2¹¹ = 1361719943 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1361721997) 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, 97265850 + ... + 97265863.

It is an arithmetic number, because the mean of its divisors is an integer number (389063428).

Almost surely, 2^1361721991 is an apocalyptic number.

1361721991 is a deficient number, since it is larger than the sum of its proper divisors (194531721).

1361721991 is an equidigital number, since it uses as much as digits as its factorization.

1361721991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 194531720.

The product of its digits is 20412, while the sum is 40.

The square root of 1361721991 is about 36901.5174620232. The cubic root of 1361721991 is about 1108.3990640171.

The spelling of 1361721991 in words is "one billion, three hundred sixty-one million, seven hundred twenty-one thousand, nine hundred ninety-one".