221626991 has 2 divisors, whose sum is σ = 221626992. Its totient is φ = 221626990.

The previous prime is 221626981. The next prime is 221627033. The reversal of 221626991 is 199626122.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-221626991 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (221626901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 110813495 + 110813496.

It is an arithmetic number, because the mean of its divisors is an integer number (110813496).

Almost surely, 2^221626991 is an apocalyptic number.

221626991 is a deficient number, since it is larger than the sum of its proper divisors (1).

221626991 is an equidigital number, since it uses as much as digits as its factorization.

221626991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 23328, while the sum is 38.

The square root of 221626991 is about 14887.1418008965. The cubic root of 221626991 is about 605.1655772472.

The spelling of 221626991 in words is "two hundred twenty-one million, six hundred twenty-six thousand, nine hundred ninety-one".