21172807 has 2 divisors, whose sum is σ = 21172808. Its totient is φ = 21172806.

The previous prime is 21172787. The next prime is 21172819. The reversal of 21172807 is 70827112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21172807 - 2²³ = 12784199 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21173807) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10586403 + 10586404.

It is an arithmetic number, because the mean of its divisors is an integer number (10586404).

Almost surely, 2^21172807 is an apocalyptic number.

21172807 is a deficient number, since it is larger than the sum of its proper divisors (1).

21172807 is an equidigital number, since it uses as much as digits as its factorization.

21172807 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1568, while the sum is 28.

The square root of 21172807 is about 4601.3918546457. The cubic root of 21172807 is about 276.6471154391.

Adding to 21172807 its reverse (70827112), we get a palindrome (91999919).

The spelling of 21172807 in words is "twenty-one million, one hundred seventy-two thousand, eight hundred seven".