21430861 has 2 divisors, whose sum is σ = 21430862. Its totient is φ = 21430860.

The previous prime is 21430859. The next prime is 21430909. The reversal of 21430861 is 16803412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15642025 + 5788836 = 3955^2 + 2406^2 .

It is a cyclic number.

It is not a de Polignac number, because 21430861 - 2¹ = 21430859 is a prime.

Together with 21430859, 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 (21430831) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10715430 + 10715431.

It is an arithmetic number, because the mean of its divisors is an integer number (10715431).

Almost surely, 2^21430861 is an apocalyptic number.

It is an amenable number.

21430861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21430861 is an equidigital number, since it uses as much as digits as its factorization.

21430861 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1152, while the sum is 25.

The square root of 21430861 is about 4629.3477942362. The cubic root of 21430861 is about 277.7665042477.

It can be divided in two parts, 214308 and 61, that added together give a square (214369 = 463²).

The spelling of 21430861 in words is "twenty-one million, four hundred thirty thousand, eight hundred sixty-one".