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%I #2 Mar 31 2012 12:38:28
%S 12,5741,2744210,15994428,21300003689580,723573111879672,
%T 1111984844349868137938112
%N Pell numbers sandwiched between two numbers having same number of divisors.
%t f[n_]:=Length[Divisors[n]]; a=1;b=0;c=0;lst={};Do[c=a+b+c;If[f[c-1]==f[c+1],AppendTo[lst,c]];a=b;b=c,{n,80}];lst
%Y Cf. A000129, A005237, A005238, A067889, A171666, A171667, A171668
%K nonn
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Dec 14 2009
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