21471661 has 2 divisors, whose sum is σ = 21471662. Its totient is φ = 21471660.

The previous prime is 21471641. The next prime is 21471677. The reversal of 21471661 is 16617412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14969161 + 6502500 = 3869^2 + 2550^2 .

It is a cyclic number.

It is not a de Polignac number, because 21471661 - 2⁷ = 21471533 is a prime.

It is a super-3 number, since 3×21471661³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21471631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10735830 + 10735831.

It is an arithmetic number, because the mean of its divisors is an integer number (10735831).

Almost surely, 2^21471661 is an apocalyptic number.

It is an amenable number.

21471661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21471661 is an equidigital number, since it uses as much as digits as its factorization.

21471661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 28.

The square root of 21471661 is about 4633.7523671426. The cubic root of 21471661 is about 277.9426628124.

The spelling of 21471661 in words is "twenty-one million, four hundred seventy-one thousand, six hundred sixty-one".