131721209 has 2 divisors, whose sum is σ = 131721210. Its totient is φ = 131721208.

The previous prime is 131721199. The next prime is 131721223. The reversal of 131721209 is 902127131.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 79477225 + 52243984 = 8915^2 + 7228^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-131721209 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (131721409) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 65860604 + 65860605.

It is an arithmetic number, because the mean of its divisors is an integer number (65860605).

Almost surely, 2^131721209 is an apocalyptic number.

It is an amenable number.

131721209 is a deficient number, since it is larger than the sum of its proper divisors (1).

131721209 is an equidigital number, since it uses as much as digits as its factorization.

131721209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 756, while the sum is 26.

The square root of 131721209 is about 11476.9860590662. The cubic root of 131721209 is about 508.8056236131.

The spelling of 131721209 in words is "one hundred thirty-one million, seven hundred twenty-one thousand, two hundred nine".