21165421 has 2 divisors, whose sum is σ = 21165422. Its totient is φ = 21165420.

The previous prime is 21165409. The next prime is 21165427. The reversal of 21165421 is 12456112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14478025 + 6687396 = 3805^2 + 2586^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21165421 is a prime.

It is a super-2 number, since 2×21165421² = 895950092214482, which contains 22 as substring.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21165392 and 21165401.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21165427) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10582710 + 10582711.

It is an arithmetic number, because the mean of its divisors is an integer number (10582711).

Almost surely, 2^21165421 is an apocalyptic number.

It is an amenable number.

21165421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21165421 is an equidigital number, since it uses as much as digits as its factorization.

21165421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 480, while the sum is 22.

The square root of 21165421 is about 4600.5892013958. The cubic root of 21165421 is about 276.6149428314.

The spelling of 21165421 in words is "twenty-one million, one hundred sixty-five thousand, four hundred twenty-one".