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 A370205 #16 Jun 21 2025 07:54:04
%S A370205 6,12,20,24,28,40,48,56,80,88,96,104,112,160,176,192,208,224,272,304,
%T A370205 320,352,368,384,416,448,464,496,544,608,640,704,736,768,832,896,928,
%U A370205 992,1088,1184,1216,1280,1312,1376,1408,1472,1504,1536,1664,1696,1792,1856,1888,1952,1984
%N A370205 Numbers j whose symmetric representation of sigma(j) consists of the single unimodal width pattern 121.
%C A370205 Every term has 2 odd divisors and has the form 2^k * p, k > 0, p prime and 2 < p < 2^(k+1), and therefore is a subsequence of A082662. The two 1's in row a(n) of the triangle of A237048 occur in positions 1 and p up to the diagonal since p <= floor( (sqrt(8*a(n) + 1) - 1)/2 ) < 2^(k+1) which represents the unimodal width pattern 121 in SRS(a(n)).
%C A370205 Numbers in this sequence divisible by 5 have the form 2^(k+2) * 5, k >= 0, the least being a(3) = 20.
%t A370205 (* function based on conditions for the odd divisors - fast computation *)
%t A370205 a370205Q[n_] := Module[{p=NestWhile[#/2&, n, EvenQ[#]&]}, PrimeQ[p]&&p^2<2n]
%t A370205 a370205[m_, n_] := Select[Range[m, n], a370205Q]
%t A370205 a370205[1, 1984]
%t A370205 (* widthPattern[ ] and support functions are defined in A341969 - slow computation *)
%t A370205 a370205[m_, n_] := Select[Range[m, n], widthPattern[#]=={1, 2, 1}&]
%t A370205 a370205[1, 1984]
%Y A370205 Cf. A082662, A235791, A237048, A237270, A237271, A237591, A237593, A249223, A262045, A341969, A342592, A342594, A342595, A342596.
%K A370205 nonn
%O A370205 1,1
%A A370205 _Hartmut F. W. Hoft_, Feb 11 2024