Is 1 4 7 11 15 20 25 ... an arithmetic sequence explain

Yes

Step-by-step explanation:

Yes, it is an arithmetic sequence. An arithmetic sequence has a certain defined pattern between numbers. If we take this sequence "1,4,7,11,15,20,25" we can see that they have a pattern: to go from 1 to 4 there are 3 numbers, so we can say it's +3. Between 4 and 7, we also have +3. However, between 7 and 11, we have +4 and the same happens with 11 and 15. Moreover, between 15 and 20, that's a +5 and 20 and 25 is another +5. So we have a +n repeating twice, which makes me conclude that this sequence goes like; +3+3+4+4+5+5+6+6+7+7+8+8+9+9... and so on...

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step-by-step explanation:

it me < 3