81561629 has 2 divisors, whose sum is σ = 81561630. Its totient is φ = 81561628.

The previous prime is 81561551. The next prime is 81561671. The reversal of 81561629 is 92616518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81036004 + 525625 = 9002^2 + 725^2 .

It is a cyclic number.

It is not a de Polignac number, because 81561629 - 2⁸ = 81561373 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 81561592 and 81561601.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81561679) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40780814 + 40780815.

It is an arithmetic number, because the mean of its divisors is an integer number (40780815).

Almost surely, 2^81561629 is an apocalyptic number.

It is an amenable number.

81561629 is a deficient number, since it is larger than the sum of its proper divisors (1).

81561629 is an equidigital number, since it uses as much as digits as its factorization.

81561629 is an evil number, because the sum of its binary digits is even.

The product of its digits is 25920, while the sum is 38.

The square root of 81561629 is about 9031.1477122235. The cubic root of 81561629 is about 433.6725800359.

The spelling of 81561629 in words is "eighty-one million, five hundred sixty-one thousand, six hundred twenty-nine".