Odd One Out means find the number which is different to other numbers--- 6,15,35,77,145
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6
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145
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15
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77
The pattern shows numbers that are 1 less than perfect squares: 15 = 4² - 1, 35 = 6² - 1, 63 would be 8² - 1, 99 would be 10² - 1. However, 6 and 77 don't fit the n² - 1 pattern (where n increases by 2). Among the given options, 145 is the largest and doesn't follow the systematic progression of the sequence.
The sequence follows a pattern of products of consecutive odd/prime-like number pairs: 6 = 2×3, 15 = 3×5, 35 = 5×7, 77 = 7×11 — each term is the product of two numbers 2 apart in a sequence of primes (2,3,5,7,11,13,...). Following the pattern, the next term should be 11×13 = 143, but the given number is 145, which breaks the pattern (145 = 5×29, not fitting the consecutive-prime-product rule). Hence 145 is the odd one out.