A077804 Deficient oblong numbers.

2, 110, 182, 506, 1406, 1892, 2162, 2756, 3422, 3782, 4556, 5402, 6806, 7310, 8930, 9506, 11342, 11990, 14042, 14762, 17030, 17822, 18632, 20306, 21170, 22052, 22952, 24806, 26732, 27722, 29756, 31862, 32942, 36290, 37442, 41006, 42230

Offset

1,1

Comments

"In 1700, Charles de Neuveglise claimed the product of two consecutive integers n(n+1) with n>=3 is abundant." - Tattersall, p. 133.

References

James J. Tattersall, Elementary Number Theory in Nine Chapters, Cambridge University Press, 2001.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1001 from Harvey P. Dale)

Charles de Neuveglise, Traité methodique et abregé de toutes les mathématiques, tome 2 (L’arithmétique ou Science des nombres), Trevoux, 1700, pp. 244-246.

Leonard Eugene Dickson, History of the Theory of Numbers, Washington, Carnegie Institution of Washington, 1919, p. 15.

Formula

a(n) = A002378(A191969(n)). - Amiram Eldar, Mar 11 2024

Mathematica

Select[Table[n(n+1), {n, 300}], DivisorSigma[1, #]<2#&] (* Harvey P. Dale, Oct 03 2011 *)

Prog

(PARI) for(n=1, 350, o=n*(n+1); if(sigma(o)<2*o, print1(o, ", ")))

Crossrefs

Intersection of A002378 and A005100.

Cf. A005101, A191969.

Sequence in context: A062656 A173372 A323250 * A063668 A006334 A093425

Adjacent sequences: A077801 A077802 A077803 * A077805 A077806 A077807

Keyword

easy,nonn

Author

Jason Earls, Dec 03 2002

Extensions

Offset corrected by Amiram Eldar, Mar 11 2024

Status

approved