%I A138238
%S A138238 0,1,0,9,16,105,336,1513,5712,23529,92752,373737,1489488,5968873,
%T A138238 23853648,95458281,381745744,1527157737,6108281424,24433824745,
%U A138238 97733900880,390938399721,1563748006480
%V A138238 0,1,0,9,-16,105,-336,1513,-5712,23529,-92752,373737,-1489488,5968873,
               -23853648,
%W A138238 95458281,-381745744,1527157737,-6108281424,24433824745,-97733900880,390938399721,
%X A138238 -1563748006480
%N A138238 Alternating sum of the squares of the first n Jacobsthal numbers.
%F A138238 G.f. : x(1+2x)/((1-x^2)(1+2x-8x^2)); a(n)=4*2^n/9-4(-4)^n/45-(-1)^n/18-3/
               10; a(n)=(13-4*J(2n+1))(-1)^n/30+4*J(n)/3-3/10, J(n)=A001045(n); 
               a(n)=sum{k=0..n (-1)^(k+1)*J(k)^2};
%Y A138238 Cf. A119283.
%Y A138238 Sequence in context: A119575 A167349 A014720 this_sequence A075373 A072470 
               A053911
%Y A138238 Adjacent sequences: A138235 A138236 A138237 this_sequence A138239 A138240 
               A138241
%K A138238 easy,sign
%O A138238 0,4
%A A138238 Paul Barry (pbarry(AT)wit.ie), Mar 07 2008