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 A275315 #48 Oct 01 2020 03:24:01 %S A275315 252,1197,2772,5292,6300,10800,13440,17856,69552,66960,69120,78624, %T A275315 84240,112320,131040,122760,147420,155520,174096,178560,194400,199584, %U A275315 322812,349272,374976,378000,446400,477603,508896,524160,635040,648000,657720,673920,648000,725760,761400,833280,890568,939600 %N A275315 Average of amicable pairs (x,y), ordered by the smaller value x given in A002025. %C A275315 Each term represents the midpoint of an interval (x,y), where x (A002025) and y (A002046) form a pair of amicable numbers (A259180). The length and radius of each interval can be found in A066539 and A162884, respectively. %C A275315 This sequence is not monotonic (specifically, not nondecreasing), since x+y (A180164) is not monotonic. For a monotonic (nondecreasing) ordering of these averages, see A275316. %C A275315 It is unknown if there exists an amicable pair where x and y have opposite parity (one is even and the other is odd). If such a pair is ever found, then the compound adjective "same-parity" will need to be added to the name of this sequence. %H A275315 Amiram Eldar, <a href="/A275315/b275315.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..142 from Timothy L. Tiffin) %H A275315 VaxaSoftware, <a href="http://www.vaxasoftware.com/doc_eduen/mat/numamigos_eng.pdf">List of amicable numbers from 1 to 20,000,000</a> [142 pairs]. %F A275315 a(n) = [A002025(n) + A002046(n)]/2 = A180164(n)/2. %e A275315 a( 1) = ( 220 + 284)/2 = 504/2 = 252. %e A275315 a( 2) = ( 1184 + 1210)/2 = 2394/2 = 1197. %e A275315 a( 3) = ( 2620 + 2924)/2 = 5544/2 = 2772. %e A275315 ... ... ... ... ... %e A275315 a( 9) = ( 63020 + 76084)/2 = 139104/2 = 69552. %e A275315 a( 10) = ( 66928 + 66992)/2 = 133920/2 = 66960. %e A275315 a( 11) = ( 67095 + 71145)/2 = 138240/2 = 69120. %e A275315 ... ... ... ... ... %e A275315 a( 15) = ( 122265 + 139815)/2 = 262080/2 = 131040. %e A275315 a( 16) = ( 122368 + 123152)/2 = 245520/2 = 122760. %e A275315 a( 17) = ( 141664 + 153176)/2 = 294840/2 = 147420. %e A275315 ... ... ... ... ... %e A275315 a( 32) = ( 609928 + 686072)/2 = 1296000/2 = 648000. %e A275315 ... ... ... ... ... %e A275315 a( 35) = ( 643336 + 652664)/2 = 1296000/2 = 648000. %e A275315 ... ... ... ... ... %e A275315 a(105) = ( 9478910 + 11049730)/2 = 20528640/2 = 10264320. %e A275315 ... ... ... ... ... %e A275315 a(109) = (10254970 + 10273670)/2 = 20528640/2 = 10264320. %e A275315 ... ... ... ... ... %e A275315 a(137) = (17754165 + 19985355)/2 = 37739520/2 = 18869760. %e A275315 a(138) = (17844255 + 19895265)/2 = 37739520/2 = 18869760. %e A275315 ... ... ... ... ... %Y A275315 Cf. A002025, A002046, A066539, A162884, A180164, A259180, A275316. %K A275315 nonn %O A275315 1,1 %A A275315 _Timothy L. Tiffin_, Jul 22 2016