131220721 has 2 divisors, whose sum is σ = 131220722. Its totient is φ = 131220720.

The previous prime is 131220701. The next prime is 131220731. The reversal of 131220721 is 127022131.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 89113600 + 42107121 = 9440^2 + 6489^2 .

It is a cyclic number.

It is not a de Polignac number, because 131220721 - 2²¹ = 129123569 is a prime.

It is not a weakly prime, because it can be changed into another prime (131220701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 65610360 + 65610361.

It is an arithmetic number, because the mean of its divisors is an integer number (65610361).

Almost surely, 2^131220721 is an apocalyptic number.

It is an amenable number.

131220721 is a deficient number, since it is larger than the sum of its proper divisors (1).

131220721 is an equidigital number, since it uses as much as digits as its factorization.

131220721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 168, while the sum is 19.

The square root of 131220721 is about 11455.1613257955. The cubic root of 131220721 is about 508.1603863032.

Adding to 131220721 its reverse (127022131), we get a palindrome (258242852).

The spelling of 131220721 in words is "one hundred thirty-one million, two hundred twenty thousand, seven hundred twenty-one".