21420761 has 2 divisors, whose sum is σ = 21420762. Its totient is φ = 21420760.

The previous prime is 21420719. The next prime is 21420793. The reversal of 21420761 is 16702412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14969161 + 6451600 = 3869^2 + 2540^2 .

It is a cyclic number.

It is not a de Polignac number, because 21420761 - 2¹⁰ = 21419737 is a prime.

It is not a weakly prime, because it can be changed into another prime (21420661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10710380 + 10710381.

It is an arithmetic number, because the mean of its divisors is an integer number (10710381).

Almost surely, 2^21420761 is an apocalyptic number.

It is an amenable number.

21420761 is a deficient number, since it is larger than the sum of its proper divisors (1).

21420761 is an equidigital number, since it uses as much as digits as its factorization.

21420761 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 672, while the sum is 23.

The square root of 21420761 is about 4628.2567992712. The cubic root of 21420761 is about 277.7228618492.

The spelling of 21420761 in words is "twenty-one million, four hundred twenty thousand, seven hundred sixty-one".