Search: id:A049452
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%I A049452
%S A049452 0,5,22,51,92,145,210,287,376,477,590,715,852,1001,1162,1335,1520,
%T A049452 1717,1926,2147,2380,2625,2882,3151,3432,3725,4030,4347,4676,5017,
%U A049452 5370,5735,6112,6501,6902,7315,7740,8177,8626,9087,9560,10045,10542
%N A049452 Pentagonal numbers with even index.
%C A049452 If Y is a 3-subset of an (2n+1)-set X then, for n>=4, a(n-1) is the number 
               of 4-subsets of X having at least two elements in common with Y. 
               - Milan R. Janjic (agnus(AT)blic.net), Dec 16 2007
%F A049452 a(n) = n*(6*n-1).
%F A049452 G.f.: A(x) = x*(5+7*x)/(1-x)^3.
%F A049452 a(n)=C(6*n,2)/3,n>=0 - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), 
               Jan 02 2007
%F A049452 a(n)=A001105(n)+A033991(n) =A033428(n)+A049450(n) = A022266(n)+A000326(n). 
               - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jun 12 2007
%F A049452 a(n)=12*n+a(n-1)-19 (with a(1)=0) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), 
               Nov 12 2009]
%e A049452 For n=2, a(2)=12*2+0-19=5; n=3, a(3)=12*3+5-19=22; n=4, a(4)=12*4+22-19=51 
               [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 12 2009]
%p A049452 [seq(binomial(6*n,2)/3,n=0..42)]; - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), 
               Jan 02 2007
%p A049452 seq(n*(6*n-1),n=0..42); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), 
               Jun 12 2007
%t A049452 s=0;lst={s};Do[s+=n++ +5;AppendTo[lst, s], {n, 0, 7!, 12}];lst [From 
               Vladimir Orlovsky (4vladimir(AT)gmail.com), Nov 16 2008]
%Y A049452 Cf. A000326, A033570, A049453.
%Y A049452 Sequence in context: A085101 A082005 A099078 this_sequence A033445 A050533 
               A064836
%Y A049452 Adjacent sequences: A049449 A049450 A049451 this_sequence A049453 A049454 
               A049455
%K A049452 nonn,easy
%O A049452 0,2
%A A049452 Joe Keane (jgk(AT)jgk.org).

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