21471217421 has 2 divisors, whose sum is σ = 21471217422. Its totient is φ = 21471217420.

The previous prime is 21471217357. The next prime is 21471217457. The reversal of 21471217421 is 12471217412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17453052100 + 4018165321 = 132110^2 + 63389^2 .

It is a cyclic number.

It is not a de Polignac number, because 21471217421 - 2⁶ = 21471217357 is a prime.

It is a super-2 number, since 2×21471217421² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21471217721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10735608710 + 10735608711.

It is an arithmetic number, because the mean of its divisors is an integer number (10735608711).

Almost surely, 2^21471217421 is an apocalyptic number.

It is an amenable number.

21471217421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21471217421 is an equidigital number, since it uses as much as digits as its factorization.

21471217421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6272, while the sum is 32.

Subtracting from 21471217421 its reverse (12471217412), we obtain a palindrome (9000000009).

The spelling of 21471217421 in words is "twenty-one billion, four hundred seventy-one million, two hundred seventeen thousand, four hundred twenty-one".