A happy prime is a prime number that is also a happy number. Thus repeated replacement of the integer by the sum of the squares of its decimal digits eventually reaches 1. The first happy primes are
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(OEIS A035497).
Happy Prime
See also
Happy Number, Prime NumberExplore with Wolfram|Alpha
References
Rivera, C. "Problems & Puzzles: Puzzle 021-Happy Primes." https://www.primepuzzles.net/puzzles/puzz_021.htm.Sloane, N. J. A. Sequence A035497 in "The On-Line Encyclopedia of Integer Sequences."Cite this as:
Weisstein, Eric W. "Happy Prime." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/HappyPrime.html