421 has 2 divisors, whose sum is σ = 422. Its totient is φ = 420.

The previous prime is 419. The next prime is 431. The reversal of 421 is 124.

421 is nontrivially palindromic in base 11 and base 15.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 225 + 196 = 15^2 + 14^2 .

It is a cyclic number.

It is not a de Polignac number, because 421 - 2^{1} = 419 is a prime.

Together with 419, it forms a pair of twin primes.

It is the 21-st Hogben number.

421 is an undulating number in base 11 and base 15.

421 is a lucky number.

It is a nialpdrome in base 10 and base 14.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (401) by changing a digit.

It is a nontrivial repunit in base 20.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 210 + 211.

It is an arithmetic number, because the mean of its divisors is an integer number (211).

421 is the 15-th centered square number.

It is an amenable number.

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

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

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

The product of its digits is 8, while the sum is 7.

The square root of 421 is about 20.5182845287. The cubic root of 421 is about 7.4948112259.

Adding to 421 its reverse (124), we get a palindrome (545).

It can be divided in two parts, 4 and 21, that added together give a square (25 = 5^{2}).

The spelling of 421 in words is "four hundred twenty-one", and thus it is an aban number and an iban number.

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