cp's OEIS Frontend

A077804 Deficient oblong numbers.

%I A077804 #20 Mar 11 2024 04:22:12
%S A077804 2,110,182,506,1406,1892,2162,2756,3422,3782,4556,5402,6806,7310,8930,
%T A077804 9506,11342,11990,14042,14762,17030,17822,18632,20306,21170,22052,
%U A077804 22952,24806,26732,27722,29756,31862,32942,36290,37442,41006,42230
%N A077804 Deficient oblong numbers.
%C A077804 "In 1700, Charles de Neuveglise claimed the product of two consecutive integers n(n+1) with n>=3 is abundant." - Tattersall, p. 133.
%D A077804 James J. Tattersall, Elementary Number Theory in Nine Chapters, Cambridge University Press, 2001.
%H A077804 Amiram Eldar, <a href="/A077804/b077804.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1001 from Harvey P. Dale)
%H A077804 Charles de Neuveglise, <a href="https://books.google.com/books?id=pmQsF89utUEC&amp;pg=PA244">Traité methodique et abregé de toutes les mathématiques</a>, tome 2 (L’arithmétique ou Science des nombres), Trevoux, 1700, pp. 244-246.
%H A077804 Leonard Eugene Dickson, <a href="https://archive.org/details/historyoftheoryo01dick_1/page/15/mode/1up">History of the Theory of Numbers</a>, Washington, Carnegie Institution of Washington, 1919, p. 15.
%F A077804 a(n) = A002378(A191969(n)). - _Amiram Eldar_, Mar 11 2024
%t A077804 Select[Table[n(n+1),{n,300}],DivisorSigma[1,#]<2#&] (* _Harvey P. Dale_, Oct 03 2011 *)
%o A077804 (PARI) for(n=1,350,o=n*(n+1); if(sigma(o)<2*o,print1(o,",")))
%Y A077804 Intersection of A002378 and A005100.
%Y A077804 Cf. A005101, A191969.
%K A077804 easy,nonn
%O A077804 1,1
%A A077804 _Jason Earls_, Dec 03 2002
%E A077804 Offset corrected by _Amiram Eldar_, Mar 11 2024