Search: id:A121051
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%I A121051
%S A121051 15,39,55,87,95,111,119,143,159,183,215,247,287,295
%N A121051 Semiprimes which are sums of 4 but no fewer nonzero squares.
%C A121051 Semiprime analogue of A007522 Primes of form 8n+7. These semiprimes must 
               all be numbers of the form 4^i(8j+7), i >= 0, j >= 0. However, for 
               positive i, 4^i(8j+7) has more than 2 prime factors (with multiplicity). 
               Hence from Legendre's corrolary to Lagrange's Four-Square Theorem, 
               this sequence is precisely Semiprimes of the form 8*k+7.
%Y A121051 A001358 intersect A004215.
%Y A121051 Cf. A001358, A004215, A007522.
%Y A121051 Sequence in context: A154988 A086096 A055131 this_sequence A139042 A020142 
               A146696
%Y A121051 Adjacent sequences: A121048 A121049 A121050 this_sequence A121052 A121053 
               A121054
%K A121051 easy,nonn,less
%O A121051 1,1
%A A121051 Jonathan Vos Post (jvospost3(AT)gmail.com), Aug 08 2006

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