21521431 has 2 divisors, whose sum is σ = 21521432. Its totient is φ = 21521430.

The previous prime is 21521419. The next prime is 21521453. The reversal of 21521431 is 13412512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21521431 - 2¹⁹ = 20997143 is a prime.

It is a super-2 number, since 2×21521431² = 926343984575522, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21521399 and 21521408.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21581431) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760715 + 10760716.

It is an arithmetic number, because the mean of its divisors is an integer number (10760716).

Almost surely, 2^21521431 is an apocalyptic number.

21521431 is a deficient number, since it is larger than the sum of its proper divisors (1).

21521431 is an equidigital number, since it uses as much as digits as its factorization.

21521431 is an evil number, because the sum of its binary digits is even.

The product of its digits is 240, while the sum is 19.

The square root of 21521431 is about 4639.1196363103. The cubic root of 21521431 is about 278.1572484763.

Adding to 21521431 its reverse (13412512), we get a palindrome (34933943).

It can be divided in two parts, 21521 and 431, that added together give a cube (21952 = 28³).

The spelling of 21521431 in words is "twenty-one million, five hundred twenty-one thousand, four hundred thirty-one".