210991421 has 2 divisors, whose sum is σ = 210991422. Its totient is φ = 210991420.

The previous prime is 210991381. The next prime is 210991433. The reversal of 210991421 is 124199012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 177928921 + 33062500 = 13339^2 + 5750^2 .

It is a cyclic number.

It is not a de Polignac number, because 210991421 - 2¹⁰ = 210990397 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 (210991621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 105495710 + 105495711.

It is an arithmetic number, because the mean of its divisors is an integer number (105495711).

Almost surely, 2^210991421 is an apocalyptic number.

It is an amenable number.

210991421 is a deficient number, since it is larger than the sum of its proper divisors (1).

210991421 is an equidigital number, since it uses as much as digits as its factorization.

210991421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1296, while the sum is 29.

The square root of 210991421 is about 14525.5437419740. The cubic root of 210991421 is about 595.3261126865.

The spelling of 210991421 in words is "two hundred ten million, nine hundred ninety-one thousand, four hundred twenty-one".