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%I #18 Aug 02 2023 16:43:36
%S 7,13,103,1009,10009,100003,1000003,10000121,100000039,1000000009,
%T 10000000033,100000000003,1000000000039,10000000000411,
%U 100000000000067,1000000000000487,10000000000000481,100000000000000003
%N Least n-digit 'happy' prime.
%C Values found by Harvey Heinz and _Jud McCranie_.
%D R. K. Guy, Unsolved Problems Number Theory, Sect. E34.
%H Bo Gyu Jeong, <a href="/A046519/b046519.txt">Table of n, a(n) for n = 1..50</a>
%H C. Rivera, <a href="http://www.primepuzzles.net/puzzles/puzz_021.htm">Related puzzle page</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/HappyNumber.html">Happy Number</a>
%o (Python)
%o from sympy import nextprime
%o def A046519(n):
%o m = 10**(n-1)
%o while (m:=nextprime(m)):
%o k = m
%o while k not in {1,37,58,89,145,42,20,4,16}:
%o k = sum((0, 1, 4, 9, 16, 25, 36, 49, 64, 81)[ord(d)-48] for d in str(k))
%o if k == 1:
%o return m # _Chai Wah Wu_, Aug 02 2023
%Y Cf. A007770, A035497.
%K nonn,base
%O 1,1
%A _Patrick De Geest_, Sep 15 1998
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