135721 has 2 divisors, whose sum is σ = 135722. Its totient is φ = 135720.
The previous prime is 135719. The next prime is 135727. The reversal of 135721 is 127531.
It is a weak prime.
It can be written as a sum of positive squares in only one way, i.e., 68121 + 67600 = 261^2 + 260^2 .
It is a cyclic number.
It is not a de Polignac number, because 135721 - 21 = 135719 is a prime.
Together with 135719, it forms a pair of twin primes.
It is a nialpdrome in base 12.
It is not a weakly prime, because it can be changed into another prime (135727) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 67860 + 67861.
It is an arithmetic number, because the mean of its divisors is an integer number (67861).
2135721 is an apocalyptic number.
135721 is the 261-st centered square number.
It is an amenable number.
135721 is a deficient number, since it is larger than the sum of its proper divisors (1).
135721 is an equidigital number, since it uses as much as digits as its factorization.
135721 is an evil number, because the sum of its binary digits is even.
The product of its digits is 210, while the sum is 19.
The square root of 135721 is about 368.4033116029. The cubic root of 135721 is about 51.3904416813.
It can be divided in two parts, 1357 and 21, that added together give a triangular number (1378 = T52).
The spelling of 135721 in words is "one hundred thirty-five thousand, seven hundred twenty-one".
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