135631721 has 2 divisors, whose sum is σ = 135631722. Its totient is φ = 135631720.

The previous prime is 135631697. The next prime is 135631723. The reversal of 135631721 is 127136531.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 135396496 + 235225 = 11636^2 + 485^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-135631721 is a prime.

Together with 135631723, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (135631723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 67815860 + 67815861.

It is an arithmetic number, because the mean of its divisors is an integer number (67815861).

Almost surely, 2^135631721 is an apocalyptic number.

It is an amenable number.

135631721 is a deficient number, since it is larger than the sum of its proper divisors (1).

135631721 is an equidigital number, since it uses as much as digits as its factorization.

135631721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3780, while the sum is 29.

The square root of 135631721 is about 11646.1032538785. The cubic root of 135631721 is about 513.7917078083.

The spelling of 135631721 in words is "one hundred thirty-five million, six hundred thirty-one thousand, seven hundred twenty-one".