42721309 has 2 divisors, whose sum is σ = 42721310. Its totient is φ = 42721308.

The previous prime is 42721307. The next prime is 42721313. The reversal of 42721309 is 90312724.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 30140100 + 12581209 = 5490^2 + 3547^2 .

It is a cyclic number.

It is not a de Polignac number, because 42721309 - 2¹ = 42721307 is a prime.

It is a super-2 number, since 2×42721309² = 3650220485346962, which contains 22 as substring.

Together with 42721307, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (42721307) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 21360654 + 21360655.

It is an arithmetic number, because the mean of its divisors is an integer number (21360655).

Almost surely, 2^42721309 is an apocalyptic number.

It is an amenable number.

42721309 is a deficient number, since it is larger than the sum of its proper divisors (1).

42721309 is an equidigital number, since it uses as much as digits as its factorization.

42721309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3024, while the sum is 28.

The square root of 42721309 is about 6536.1539914540. The cubic root of 42721309 is about 349.5812924942.

It can be divided in two parts, 427 and 21309, that added together give a triangular number (21736 = T₂₀₈).

The spelling of 42721309 in words is "forty-two million, seven hundred twenty-one thousand, three hundred nine".