42006721 has 2 divisors, whose sum is σ = 42006722. Its totient is φ = 42006720.

The previous prime is 42006719. The next prime is 42006737. The reversal of 42006721 is 12760024.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 41216400 + 790321 = 6420^2 + 889^2 .

It is a cyclic number.

It is not a de Polignac number, because 42006721 - 2¹ = 42006719 is a prime.

Together with 42006719, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 42006692 and 42006701.

It is not a weakly prime, because it can be changed into another prime (42006751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 21003360 + 21003361.

It is an arithmetic number, because the mean of its divisors is an integer number (21003361).

Almost surely, 2^42006721 is an apocalyptic number.

It is an amenable number.

42006721 is a deficient number, since it is larger than the sum of its proper divisors (1).

42006721 is an equidigital number, since it uses as much as digits as its factorization.

42006721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 672, while the sum is 22.

The square root of 42006721 is about 6481.2592140725. The cubic root of 42006721 is about 347.6212050672.

Adding to 42006721 its reverse (12760024), we get a palindrome (54766745).

The spelling of 42006721 in words is "forty-two million, six thousand, seven hundred twenty-one".