A356179 - OEIS

A356179

Positions of records in A279497, i.e., integers whose number of pentagonal divisors sets a new record.

1, 5, 35, 70, 210, 420, 2310, 4620, 18480, 32340, 60060, 120120, 240240, 720720, 1141140, 2042040, 4084080, 4564560, 13693680, 19399380, 38798760, 77597520, 232792560, 387987600

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OFFSET

1,2

COMMENTS

The first fourteen terms are the same as A356132; then a(15) = 1141140 while A356132(15) = 1261260.

Corresponding records of number of pentagonal divisors are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, ...

LINKS

Table of n, a(n) for n=1..24.

EXAMPLE

210 is in the sequence because A279497(210) = 5 is larger than any earlier value in A279497.

MATHEMATICA

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 *)

PROG

(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

CROSSREFS

Cf. A000326, A279497, A356132.

Similar sequences: A046952, A093036, A350756, A355595.

Sequence in context: A115707 A117793 A145920 * A356132 A153785 A369812

Adjacent sequences: A356176 A356177 A356178 * A356180 A356181 A356182

KEYWORD

nonn,more

AUTHOR

Bernard Schott, Jul 28 2022

EXTENSIONS

a(23)-a(24) from David A. Corneth, Jul 28 2022

STATUS

approved