Search: id:A156619
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%I A156619
%S A156619 7,18,32,43,57,68,82,93,107,118,132,143,157,168,182,193,207,218,232,243,
%T A156619 257,268,282,293,307,318,332,343,357,368,382,393,407,418,432,443,457,
%U A156619 468,482,493,507,518,532,543,557,568,582,593,607,618,632,643,657,668
%N A156619 Numbers n such that n^2+1=0 mod (5^2)
%C A156619 Also, if a(1)=7, a(2)=18, a(n)=2*a(n-1)-a(n-2)-3 (if n is even); a(n)=2*a(n-1)-a(n-2)+3 
               (if n is odd); example: a(3)=2*18-7+3=32; a(4)=2*32-18-3=43; a(5)=2*43-32+3=57; 
               a(6)=2*57-43-3=68; the sequence (7,18,32,43,57,68,82,93) repeat to 
               (107,118,..,) (207,218,..,) (307,318,..,) (407,418,...,) and so on
%C A156619 Except for the first term, a(n)=25*n-a(n-1), (with a(1)=18) [From Vincenzo 
               Librandi (vincenzo.librandi(AT)tin.it), Oct 23 2009]
%F A156619 n^2+1=0 mod (5^2)
%F A156619 a(n)=a(n-1)+a(n-2)-a(n-3) = 25*n/2-25/4-3*(-1)^n/4. G.f.: x(7+11x+7x^2)/
               ((1+x)(1-x)^2). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), 
               Feb 19 2009]
%e A156619 For n=7, 50=0 mod (25); n=18, 325=0 mod (25); n=468, 219025=0 mod (25).
%Y A156619 Sequence in context: A103571 A103572 A049532 this_sequence A033537 A000566 
               A133673
%Y A156619 Adjacent sequences: A156616 A156617 A156618 this_sequence A156620 A156621 
               A156622
%K A156619 nonn
%O A156619 1,1
%A A156619 Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Feb 11 2009

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