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 A331628 #16 Dec 29 2024 04:09:35
%S A331628 15,21,45,50,52,63,75,99,105,117,135,182,190,195,230,231,266,273,315,
%T A331628 375,405,435,495,585,592,656,688,850,891,950,1155,1215,1305,1365,1395,
%U A331628 1612,1755,1845,1862,1875,1892,1989,2079,2295,2312,2332,2336,2350,2366,2475
%N A331628 Integers that are exactly 2-deficient-perfect numbers.
%C A331628 Numbers k that have 2 distinct proper divisors, d_1 and d_2, such that sigma(k) = 2*k - (d_1 + d_2). - _Amiram Eldar_, Dec 29 2024
%H A331628 Amiram Eldar, <a href="/A331628/b331628.txt">Table of n, a(n) for n = 1..1000</a>
%H A331628 FengJuan Chen, <a href="http://math.colgate.edu/~integers/t37/t37.Abstract.html">On Exactly k-deficient-perfect Numbers</a>, Integers, 19 (2019), Article A37, 1-9.
%e A331628 117 is an exactly 2-deficient-perfect number with d1=13 and d2=39: sigma(117) = 182 = 2*117 - (13 + 39). See Theorem 1 p. 2 of FengJuan Chen.
%t A331628 def2[n_] := Catch@Block[{s = 2*n - DivisorSigma[1, n], d}, If[s > 0, d = Most@ Divisors@ n; Do[If[s == d[[i]] + d[[j]], Throw@ True], {i, 2, Length@ d}, {j, i-1}]; False]]; Select[Range[2500], def2] (* _Giovanni Resta_, Jan 23 2020 *)
%Y A331628 Cf. A000203 (sigma), A271816 (deficient-perfect numbers (k=1)), A331627 (k-deficient-perfect), A331629 (3-deficient-perfect).
%K A331628 nonn
%O A331628 1,1
%A A331628 _Michel Marcus_, Jan 23 2020
%E A331628 More terms from _Giovanni Resta_, Jan 23 2020