This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A276565 #18 Dec 01 2016 04:21:32 %S A276565 56,552,870,1056,1190,1640,1892,2652,4032,5256,5402,6806,8372,9120, %T A276565 9506,9702,10920,11772,12656,12882,15006,15252,15500,16256,16770, %U A276565 17556,18632,23256,24492,27722,29070,30800,33306,33672,34410,36290,40200,40602,44310,45582,46872,49506 %N A276565 Oblong numbers n such that n - 1 and n + 1 are both semiprime. %C A276565 Intersection of A002378 and A124936. - _Michel Marcus_, Nov 26 2016 %H A276565 Robert Israel, <a href="/A276565/b276565.txt">Table of n, a(n) for n = 1..10000</a> %e A276565 1640 is oblong (1640 = 40*41) and 1639 = 11*149, 1641 = 3*547 are both semiprime. %p A276565 select(t -> numtheory:-bigomega(t+1)=2 and numtheory:-bigomega(t-1)=2, [seq(i*(i+1),i=1..1000)]); # _Robert Israel_, Nov 28 2016 %o A276565 (PARI) for(i=1,250,n=i*(i+1);if(bigomega(n-1)==2&&bigomega(n+1)==2,print1(n,", "))) %Y A276565 Cf. A002378, A124936. %Y A276565 Cf. A001597, A108278, A121898, A167023, A268043, A276564. %K A276565 nonn %O A276565 1,1 %A A276565 _Antonio Roldán_, Nov 16 2016