21565667 has 2 divisors, whose sum is σ = 21565668. Its totient is φ = 21565666.

The previous prime is 21565633. The next prime is 21565699. The reversal of 21565667 is 76656512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21565667 - 2¹² = 21561571 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21565667.

It is not a weakly prime, because it can be changed into another prime (21565567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10782833 + 10782834.

It is an arithmetic number, because the mean of its divisors is an integer number (10782834).

Almost surely, 2^21565667 is an apocalyptic number.

21565667 is a deficient number, since it is larger than the sum of its proper divisors (1).

21565667 is an equidigital number, since it uses as much as digits as its factorization.

21565667 is an evil number, because the sum of its binary digits is even.

The product of its digits is 75600, while the sum is 38.

The square root of 21565667 is about 4643.8849038278. The cubic root of 21565667 is about 278.3476965190.

The spelling of 21565667 in words is "twenty-one million, five hundred sixty-five thousand, six hundred sixty-seven".