21012421 has 2 divisors, whose sum is σ = 21012422. Its totient is φ = 21012420.

The previous prime is 21012419. The next prime is 21012449. The reversal of 21012421 is 12421012.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20930625 + 81796 = 4575^2 + 286^2 .

It is a cyclic number.

It is not a de Polignac number, because 21012421 - 2¹ = 21012419 is a prime.

Together with 21012419, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21012401) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10506210 + 10506211.

It is an arithmetic number, because the mean of its divisors is an integer number (10506211).

Almost surely, 2^21012421 is an apocalyptic number.

It is an amenable number.

21012421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21012421 is an equidigital number, since it uses as much as digits as its factorization.

21012421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 21012421 is about 4583.9307368240. The cubic root of 21012421 is about 275.9468015160.

Adding to 21012421 its reverse (12421012), we get a palindrome (33433433).

The spelling of 21012421 in words is "twenty-one million, twelve thousand, four hundred twenty-one".