Should I contact my biological grandfather I’ve never met?

My grandmother divorced my biological grandfather over 40 years ago and I’ve never met him as my family has no contact with him whatsoever. He is almost 80 years old and I don’t know anyway to contact him because he doesn’t know he has a granddaughter and I am scared he might not want to hear from me at all because what happened between him and my grandma. But I still want a chance to know him so I was wanting to ask it I should send him a birthday card since his birthday is coming up. I found his address online so I wanted to reach out to him that way hoping he will send me a letter back or something. Is this a crazy idea?

Should I contact my biological grandfather I’ve never met?
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