Search: id:A124080
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%I A124080
%S A124080 0,10,30,60,100,150,210,280,360,450,550,660,780,910,1050,1200,1360,1530,
%T A124080 1710,1900,2100,2310,2530,2760,3000,3250,3510,3780,4060,4350,4650,4960,
%U A124080 5280,5610,5950,6300,6660,7030,7410,7800,8200,8610,9030,9460,9900,10350
%N A124080 10 times triangular numbers.
%C A124080 If Y is a 5-subset of an n-set X then, for n>=5, a(n-4) is equal to the 
               number of 5-subsets of X having exactly three elements in common 
               with Y. Y is a 5-subset of an n-set X then, for n>=6, a(n-6) is the 
               number of (n-5)-subsets of X having exactly two elements in common 
               with Y.lso, if - Milan R. Janjic (agnus(AT)blic.net), Dec 28 2007
%C A124080 Except for the first term, a(n)=10*n+a(n-1), (with a(1)=10) [From Vincenzo 
               Librandi (vincenzo.librandi(AT)tin.it), Oct 24 2009]
%F A124080 a(n)=10*C(n,2), n>=1
%F A124080 a(n)=A049598-A002378. - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), 
               Mar 06 2007
%F A124080 a(n)=n*(n+1)*5, n>=0 . - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), 
               Mar 06 2007
%F A124080 a(n) = 5n^2 + 5n = A000217(n)*10 = A002378(n)*5 = A028895(n)*2. [From 
               Omar E. Pol (info(AT)polprimos.com), Dec 12 2008]
%F A124080 a(n)=10*n+a(n-1)-10 (with a(1)=0) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), 
               Nov 12 2009]
%e A124080 For n=2, a(2)=10*2-0-10=10; n=3, a(3)=10*3+10-10=30; n=4, a(4)=10*4+30-10=60 
               [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 12 2009]
%p A124080 [seq(10*binomial(n,2),n=1..51)];
%p A124080 seq(n*(n+1)*5, n=0..39); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), 
               Mar 06 2007
%t A124080 s=0;lst={s};Do[s+=n++ +10;AppendTo[lst, s], {n, 0, 8!, 10}];lst [From 
               Vladimir Orlovsky (4vladimir(AT)gmail.com), Nov 17 2008]
%Y A124080 Cf. A028895, A046092, A045943, A002378, A028896, A024966, A033996, A027468.
%Y A124080 Cf. A002378, A049598.
%Y A124080 Cf. A000217. [From Omar E. Pol (info(AT)polprimos.com), Dec 12 2008]
%Y A124080 Sequence in context: A096844 A031299 A104044 this_sequence A034127 A005052 
               A057344
%Y A124080 Adjacent sequences: A124077 A124078 A124079 this_sequence A124081 A124082 
               A124083
%K A124080 easy,nonn
%O A124080 0,2
%A A124080 Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Nov 24 2006

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