A379095 -id:A379095 - cp's OEIS frontend

A379096 Waterproof numbers >= 60.

61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 121

Offset: 1

Peter Luschny, Dec 16 2024

nonn

All nonnegative numbers less than 60 are waterproof.
Zero and one are waterproof numbers by convention. Numbers that admit a prime factorization are waterproof if their water capacity is 0. (The water capacity of a number is defined in A275339.)
If the factors p_i^e_i in the canonical prime factorization of n are weakly ascending or weakly descending, then n is waterproof.
A number is waterproof if and only if it equals its waterproof hull (A379098). The waterproof hull h(n) of n is the smallest waterproof number that n divides.
Numbers that are not waterproof are listed in A379097.

			Numbers having at most two distinct prime factors (A070915) are waterproof. The primorials (A002110) are waterproof.
48300 has a water capacity of 17 and so is not waterproof. The waterproof hull of 48300 is 1014300.

Cf. A275339, A379094, A379095, A379097, A379098.

# The function 'water_capacity' is defined in A275339.
is_waterproof := n -> ifelse(n < 2, true, is(water_capacity(n) = 0)):
select(is_waterproof, [seq(60..121)]);

# The function 'WaterCapacity' is defined in A275339.
print([n for n in range(60, 122) if WaterCapacity(n) == 0])

A379098 The waterproof hulls of numbers that are not waterproof (A379097).

Original entry on oeis.org

180, 252, 360, 396, 468, 504, 612, 684, 720, 792, 828, 1400, 900, 936, 1575, 1008, 1044, 1116, 1224, 6300, 2200, 1332, 1368, 1440, 1476, 2475, 1548, 2600, 4752, 1656, 2800, 1692, 2925, 1764, 1800, 4312, 5616, 3150, 1908, 9900, 2016, 3400, 4851, 2088, 2124, 5096

Offset: 1

Peter Luschny, Dec 16 2024

nonn

The waterproof hull h(k) of k is the smallest waterproof number that k divides. Zero and one are waterproof numbers by convention. Numbers that admit a prime factorization are waterproof if their water capacity is 0. (The water capacity of a number is defined in A275339.)

Cf. A275339, A379095, A379096, A379097.

# Using function "WaterCapacity" from A275339.
def s(n: int) -> int:
    j = n
    while True:
        if WaterCapacity(j) == 0 and j % n == 0: return j
        j += n
print([s(n) for n in range(1, 700) if WaterCapacity(n) > 0])

A379093 Numbers whose factors in the canonical prime factorization neither increase weakly nor decrease weakly but are waterproof. (Terms of A379094 but not of A379097.)

Original entry on oeis.org

90, 126, 180, 252, 270, 350, 360, 378, 504, 525, 540, 550, 594, 650, 700, 702, 756, 810, 825, 850, 918, 950, 975, 1026, 1050, 1078, 1080, 1100, 1134, 1150, 1188, 1242, 1274, 1275, 1300, 1350, 1400, 1404, 1425, 1512, 1575, 1617, 1620, 1650, 1666, 1700, 1725

Offset: 1

Peter Luschny, Dec 17 2024

nonn

Michael De Vlieger, Table of n, a(n) for n = 1..10000

Cf. A379094, A379095, A379096, A379097.

# Using functions 'isA379094' and 'is_not_waterproof' (from A379097).
A := select(isA379094, {seq(1..1800)}):
B := select(is_not_waterproof, {seq(1..1800)}):
A minus B;

nn = 1725; s = Select[Range[nn], Nor[SquareFreeQ[#], PrimePowerQ[#]] &];
Select[s, Function[f, And[NoneTrue[{Sort[f], ReverseSort[f]}, # == f &],
  Total[(f //. {a___, b_, c__, d_, e___} /;
    AllTrue[{c}, And[# < b, # < d] &] :>
      {a, b, Sequence @@ Table[Min[b, d], {Length[{c}] } ], d, e}) - f] == 0] ]
[Power @@@ FactorInteger[#]] &] (* Michael De Vlieger, Dec 18 2024, after Jean-François Alcover at A275339 *)

cp's OEIS Frontend

A379096 Waterproof numbers >= 60.

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A379098 The waterproof hulls of numbers that are not waterproof (A379097).

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A379093 Numbers whose factors in the canonical prime factorization neither increase weakly nor decrease weakly but are waterproof. (Terms of A379094 but not of A379097.)

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