21572251 has 2 divisors, whose sum is σ = 21572252. Its totient is φ = 21572250.

The previous prime is 21572237. The next prime is 21572261. The reversal of 21572251 is 15227512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21572251 is a prime.

It is not a weakly prime, because it can be changed into another prime (21572231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10786125 + 10786126.

It is an arithmetic number, because the mean of its divisors is an integer number (10786126).

Almost surely, 2^21572251 is an apocalyptic number.

21572251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21572251 is an equidigital number, since it uses as much as digits as its factorization.

21572251 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1400, while the sum is 25.

The square root of 21572251 is about 4644.5937389615. The cubic root of 21572251 is about 278.3760201620.

Adding to 21572251 its reverse (15227512), we get a palindrome (36799763).

The spelling of 21572251 in words is "twenty-one million, five hundred seventy-two thousand, two hundred fifty-one".