221306531 has 2 divisors, whose sum is σ = 221306532. Its totient is φ = 221306530.

The previous prime is 221306473. The next prime is 221306539. The reversal of 221306531 is 135603122.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-221306531 is a prime.

It is a super-2 number, since 2×221306531² = 97953161326507922, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 221306497 and 221306506.

It is not a weakly prime, because it can be changed into another prime (221306539) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 110653265 + 110653266.

It is an arithmetic number, because the mean of its divisors is an integer number (110653266).

Almost surely, 2^221306531 is an apocalyptic number.

221306531 is a deficient number, since it is larger than the sum of its proper divisors (1).

221306531 is an equidigital number, since it uses as much as digits as its factorization.

221306531 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1080, while the sum is 23.

The square root of 221306531 is about 14876.3749280529. The cubic root of 221306531 is about 604.8737582373.

Adding to 221306531 its reverse (135603122), we get a palindrome (356909653).

The spelling of 221306531 in words is "two hundred twenty-one million, three hundred six thousand, five hundred thirty-one".