21471781 has 2 divisors, whose sum is σ = 21471782. Its totient is φ = 21471780.

The previous prime is 21471773. The next prime is 21471787. The reversal of 21471781 is 18717412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19624900 + 1846881 = 4430^2 + 1359^2 .

It is a cyclic number.

It is not a de Polignac number, because 21471781 - 2³ = 21471773 is a prime.

It is a super-2 number, since 2×21471781² = 922074758623922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21471787) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10735890 + 10735891.

It is an arithmetic number, because the mean of its divisors is an integer number (10735891).

Almost surely, 2^21471781 is an apocalyptic number.

It is an amenable number.

21471781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21471781 is an equidigital number, since it uses as much as digits as its factorization.

21471781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3136, while the sum is 31.

The square root of 21471781 is about 4633.7653155938. The cubic root of 21471781 is about 277.9431805965.

The spelling of 21471781 in words is "twenty-one million, four hundred seventy-one thousand, seven hundred eighty-one".