%I #19 Jul 30 2022 08:20:36
%S 1,5,35,70,210,420,2310,4620,18480,32340,60060,120120,240240,720720,
%T 1141140,2042040,4084080,4564560,13693680,19399380,38798760,77597520,
%U 232792560,387987600
%N Positions of records in A279497, i.e., integers whose number of pentagonal divisors sets a new record.
%C The first fourteen terms are the same as A356132; then a(15) = 1141140 while A356132(15) = 1261260.
%C Corresponding records of number of pentagonal divisors are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, ...
%e 210 is in the sequence because A279497(210) = 5 is larger than any earlier value in A279497.
%t f[n_] := DivisorSum[n, 1 &, IntegerQ[(1 + Sqrt[1 + 24*#])/6] &]; fm = -1; s = {}; Do[If[(fn = f[n]) > fm, fm = fn; AppendTo[s, n]], {n, 1, 10^5}]; s (* _Amiram Eldar_, Jul 28 2022 *)
%o (PARI) lista(nn) = my(m=0); for (n=1, nn, my(new = sumdiv(n, d, ispolygonal(d, 5))); if (new > m, m = new; print1(n, ", "));); \\ _Michel Marcus_, Jul 28 2022
%Y Cf. A000326, A279497, A356132.
%Y Similar sequences: A046952, A093036, A350756, A355595.
%K nonn,more
%O 1,2
%A _Bernard Schott_, Jul 28 2022
%E a(23)-a(24) from _David A. Corneth_, Jul 28 2022