21401531 has 2 divisors, whose sum is σ = 21401532. Its totient is φ = 21401530.

The previous prime is 21401473. The next prime is 21401539. The reversal of 21401531 is 13510412.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21401531 - 2¹⁰ = 21400507 is a prime.

It is a super-2 number, since 2×21401531² = 916051058287922, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21401539) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10700765 + 10700766.

It is an arithmetic number, because the mean of its divisors is an integer number (10700766).

Almost surely, 2^21401531 is an apocalyptic number.

21401531 is a deficient number, since it is larger than the sum of its proper divisors (1).

21401531 is an equidigital number, since it uses as much as digits as its factorization.

21401531 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 120, while the sum is 17.

The square root of 21401531 is about 4626.1788767837. The cubic root of 21401531 is about 277.6397305112.

Adding to 21401531 its reverse (13510412), we get a palindrome (34911943).

The spelling of 21401531 in words is "twenty-one million, four hundred one thousand, five hundred thirty-one".