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%I #12 Aug 31 2020 02:07:39
%S 53,263,1103,6563,4253,49613,38273,1041863,344453,60775313,109395563,
%T 119601563,151903553,325507613,3797588813,202622460863,17437907813,
%U 11299764263,20339575673,282494106563,1186475247563,5932376237813,29661881189063,8237528147363,14827550665253
%N a(n) is the least prime of the form (3^r*5^s*7^t + 1)/2, r, s, t > 0, r + s + t = n.
%H David A. Corneth, <a href="/A337428/b337428.txt">Table of n, a(n) for n = 3..506</a>
%e a(3) = 53: (3*5*7+1)/2 = 106/2 is prime.
%e a(4) = 263: The first choice of exponents leads to the composite (3^2*5*7+1)/2 = 158, but the next choice (3*5^2*7+1)/2 = 526/2 is prime.
%o (PARI) seqpp (3,3,1,27) \\ using function seqpp defined in A337427
%Y Cf. A337423, A337425, A337427.
%K nonn
%O 3,1
%A _Hugo Pfoertner_, Aug 29 2020