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A281875 Least k such that phi(k) is the sum of two primes in exactly n ways, or 0 if no such k exists. 2

%I

%S 1,5,11,23,37,65,61,79,103,161,127,157,143,199,181,307,277,313,241,

%T 211,409,341,379,487,331,623,577,551,463,527,421,571,601,673,829,757,

%U 877,997,1571,691,1039,631,1009,961,869,967,1543,989,1057,1247,2411,899,991,1303,1147,1231,1999

%N Least k such that phi(k) is the sum of two primes in exactly n ways, or 0 if no such k exists.

%C Note that this sequence is not the subsequence of A037143; i.e., a(318) = 7^3 * 47.

%H Chai Wah Wu, <a href="/A281875/b281875.txt">Table of n, a(n) for n = 0..10000</a>

%e a(3) = 23 because phi(23) = 22 = 3 + 19 = 5 + 17 = 11 + 11 and 23 is the least number with this property.

%Y Cf. A000010, A001172, A023036, A281816.

%K nonn,look

%O 0,2

%A _Altug Alkan_, Feb 01 2017

%E a(0) = 1 prepended by _Chai Wah Wu_, Feb 03 2017

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Last modified August 14 01:00 EDT 2020. Contains 336473 sequences. (Running on oeis4.)