21051421 has 2 divisors, whose sum is σ = 21051422. Its totient is φ = 21051420.

The previous prime is 21051403. The next prime is 21051427. The reversal of 21051421 is 12415012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20602521 + 448900 = 4539^2 + 670^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21051421 is a prime.

It is a super-2 number, since 2×21051421² = 886324652238482, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21051395 and 21051404.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21051427) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10525710 + 10525711.

It is an arithmetic number, because the mean of its divisors is an integer number (10525711).

Almost surely, 2^21051421 is an apocalyptic number.

It is an amenable number.

21051421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21051421 is an equidigital number, since it uses as much as digits as its factorization.

21051421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 80, while the sum is 16.

The square root of 21051421 is about 4588.1827557324. The cubic root of 21051421 is about 276.1174192332.

Adding to 21051421 its reverse (12415012), we get a palindrome (33466433).

The spelling of 21051421 in words is "twenty-one million, fifty-one thousand, four hundred twenty-one".