Aptitude - Odd Man Out and Series - Discussion

Why not 73?

81 is the only one which is divisible by 3.

Read the answer properly, it say that except 81 all are prime number. To all genius.

81 is divisible by 9, so it isn't a prime number. 9x9=81. the rest of the numbers can not be divided into evenly without a remainder. For example 5 is a prime because if you divide it by 2 you will have a remainder. 5 is only divisible by 5 or by 1.

also stated above was the formula: tn= t(n-1)+2n
where n= 1,2,3,4,...etc.
and t= 41,43,47,53,...etc.

If you plug in the numbers it doesn't equal the 2nd term which is 43.
let t= 1st term 41
n= 1

Example with above formula:tn= 41(1-1)+2(1)
41(0)+2 = 2?
I do understand t+2n
41+2(1)= 43
43+2(2)= 47
47+2(3)= 53

I am not trying to be picky, I was really trying to understand.
thanks for the above solutions!

None of them except 81 are perfect squares. So, it will be the right answer.

All the numbers are prime numbers except 81.

Prime number series is 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997 etc.

t = 41 + 2 * 1 = 43
t = 43 + 2 * 2 = 47
t = 47 + 2 * 3 = 53
t = 53 + 2 * 4 = 61
t = 61 + 2 * 5 = 71
t = 71 + 2 * 6 = 83.

In the given Series there 73 followed by 71, so the answer must be 73.

Answer 81 is correct. Because except 81, all other numbers are a prime number.

Yes, I agree with Sandeep Shenoy.

Why its ans can't be 47?

41 4>1
43 4>3
47 4<7
53 5>3
61 6>1
71 7>1
73 7>3
81 8>1

Every 10th digit no is more than except 47, so the answer is 47. Why this answer is wrong?