SOLUTION: how many positive integers from 1 to 400 inclusive have exactly three positive integral factors?

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Question 1000049: how many positive integers from 1 to 400 inclusive have exactly three positive integral factors?
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
how many positive integers from 1 to 400 inclusive have exactly three positive integral factors?
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If 1 is not included as a factor:
2*2*5
2*2*5
2*2*7
2*2*11
2*2*13
2*2*17
2*2*19
2*2*23
2*2*29
2*2*31
2*2*37
2*2*47
2*2*53
2*2*59
2*2*61
2*2*67
2*2*71
2*2*73
2*2*79
2*2*83
2*2*89
2*2*97
------
2*3*5
2*3*7
2*3*11
2*3*13
2*3*17
2*3*19
2*3*23
2*3*29
2*3*31
2*3*37
2*3*47
2*3*53
2*3*59
2*3*61
---
2*5*5
2*5*7
2*5*11
2*5*13
2*5*17
2*5*19
2*5*23
2*5*29
2*5*31
2*5*37
------
2*7*7
2*7*11
2*7*13
2*7*17
2*7*19
2*7*23
------
2*11*11
2*11*13
2*11*17
------
3*5*5
3*5*7
3*5*11
3*5*13
3*5*17
3*5*19
3*5*23
------
3*7*7
3*7*11
3*7*13
3*7*17
3*7*19
------
5*7*7
5*7*11
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You can count them.