21427639 has 2 divisors, whose sum is σ = 21427640. Its totient is φ = 21427638.

The previous prime is 21427621. The next prime is 21427643. The reversal of 21427639 is 93672412.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21427639 - 2⁹ = 21427127 is a prime.

It is a super-2 number, since 2×21427639² = 918287426228642, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21427669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10713819 + 10713820.

It is an arithmetic number, because the mean of its divisors is an integer number (10713820).

Almost surely, 2^21427639 is an apocalyptic number.

21427639 is a deficient number, since it is larger than the sum of its proper divisors (1).

21427639 is an equidigital number, since it uses as much as digits as its factorization.

21427639 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18144, while the sum is 34.

The square root of 21427639 is about 4628.9997839706. Note that the first 3 decimals coincide. The cubic root of 21427639 is about 277.7525833801.

The spelling of 21427639 in words is "twenty-one million, four hundred twenty-seven thousand, six hundred thirty-nine".