21630421 has 2 divisors, whose sum is σ = 21630422. Its totient is φ = 21630420.

The previous prime is 21630391. The next prime is 21630439. The reversal of 21630421 is 12403612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21622500 + 7921 = 4650^2 + 89^2 .

It is a cyclic number.

It is not a de Polignac number, because 21630421 - 2¹⁷ = 21499349 is a prime.

It is a super-2 number, since 2×21630421² = 935750225274482, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21630451) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10815210 + 10815211.

It is an arithmetic number, because the mean of its divisors is an integer number (10815211).

Almost surely, 2^21630421 is an apocalyptic number.

It is an amenable number.

21630421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21630421 is an equidigital number, since it uses as much as digits as its factorization.

21630421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 19.

The square root of 21630421 is about 4650.8516424414. The cubic root of 21630421 is about 278.6260110697.

The spelling of 21630421 in words is "twenty-one million, six hundred thirty thousand, four hundred twenty-one".