A237824
Number of partitions of n such that 2*(least part) >= greatest part.
Original entry on oeis.org
1, 2, 3, 4, 5, 7, 7, 10, 11, 13, 14, 19, 18, 23, 25, 29, 30, 38, 37, 46, 48, 54, 57, 70, 69, 80, 85, 97, 100, 118, 118, 137, 144, 159, 168, 193, 195, 220, 233, 259, 268, 303, 311, 348, 367, 399, 419, 469, 483, 532, 560, 610, 639, 704, 732, 801, 841, 908, 954
Offset: 1
a(6) = 7 counts these partitions: 6, 42, 33, 222, 2211, 21111, 111111.
From _Gus Wiseman_, May 14 2023: (Start)
The a(1) = 1 through a(8) = 10 partitions such that 2*(least part) >= greatest part:
(1) (2) (3) (4) (5) (6) (7) (8)
(11) (21) (22) (32) (33) (43) (44)
(111) (211) (221) (42) (322) (53)
(1111) (2111) (222) (2221) (332)
(11111) (2211) (22111) (422)
(21111) (211111) (2222)
(111111) (1111111) (22211)
(221111)
(2111111)
(11111111)
The a(1) = 1 through a(8) = 10 partitions whose greatest part appears at a middle position:
(1) (2) (3) (4) (5) (6) (7) (8)
(11) (21) (22) (32) (33) (43) (44)
(111) (31) (41) (42) (52) (53)
(1111) (221) (51) (61) (62)
(11111) (222) (331) (71)
(2211) (2221) (332)
(111111) (1111111) (2222)
(3311)
(22211)
(11111111)
(End)
These partitions have ranks
A362981.
-
z = 60; q[n_] := q[n] = IntegerPartitions[n];
Table[Count[q[n], p_ /; 2 Min[p] < Max[p]], {n, z}] (* A237820 *)
Table[Count[q[n], p_ /; 2 Min[p] <= Max[p]], {n, z}] (* A237821 *)
Table[Count[q[n], p_ /; 2 Min[p] == Max[p]], {n, z}] (* A118096 *)
Table[Count[q[n], p_ /; 2 Min[p] > Max[p]], {n, z}] (* A053263 *)
Table[Count[q[n], p_ /; 2 Min[p] >= Max[p]], {n, z}] (* this sequence *)
(* or *)
nmax = 100; Rest[CoefficientList[Series[Sum[x^k/Product[1 - x^j, {j,k,2*k}], {k, 1, nmax}], {x, 0, nmax}], x]] (* Vaclav Kotesovec, Jun 13 2025 *)
(* or *)
nmax = 100; p = 1; s = 0; Do[p = Simplify[p*(1 - x^(2*k - 1))*(1 - x^(2*k))/(1 - x^k)]; p = Normal[p + O[x]^(nmax+1)]; s += x^k/(1 - x^k)/p;, {k, 1, nmax}]; Rest[CoefficientList[Series[s, {x, 0, nmax}], x]] (* Vaclav Kotesovec, Jun 14 2025 *)
-
N=60; x='x+O('x^N);
gf = sum(m=1, N, (x^m)/(1-x^m)) + sum(i=1, N, sum(j=1, i, x^((2*i)+j)/prod(k=0, j, 1 - x^(k+i))));
Vec(gf) \\ John Tyler Rascoe, Mar 07 2024
A237821
Number of partitions of n such that 2*(least part) <= greatest part.
Original entry on oeis.org
0, 0, 1, 2, 4, 7, 11, 16, 25, 35, 48, 68, 92, 123, 164, 216, 282, 367, 471, 604, 769, 975, 1225, 1542, 1924, 2395, 2968, 3669, 4514, 5547, 6781, 8280, 10071, 12229, 14796, 17881, 21537, 25902, 31066, 37206, 44443, 53021, 63098, 74995, 88946, 105350, 124533
Offset: 1
a(6) = 7 counts these partitions: 51, 42, 411, 321, 3111, 2211, 21111.
From _Gus Wiseman_, May 15 2023: (Start)
The a(3) = 1 through a(8) = 16 partitions wirth 2*(least part) <= greatest part:
(21) (31) (41) (42) (52)
(211) (221) (51) (61)
(311) (321) (331)
(2111) (411) (421)
(2211) (511)
(3111) (2221)
(21111) (3211)
(4111)
(22111)
(31111)
(211111)
The a(3) = 1 through a(8) = 16 partitions with different median from maximum:
(21) (31) (32) (42) (43)
(211) (41) (51) (52)
(311) (321) (61)
(2111) (411) (322)
(2211) (421)
(3111) (511)
(21111) (3211)
(4111)
(22111)
(31111)
(211111)
(End)
These partitions have ranks
A069900.
The conjugate partitions have ranks
A362980.
-
z = 60; q[n_] := q[n] = IntegerPartitions[n];
Table[Count[q[n], p_ /; 2 Min[p] < Max[p]], {n, z}] (* A237820 *)
Table[Count[q[n], p_ /; 2 Min[p] <= Max[p]], {n, z}] (* A237821 *)
Table[Count[q[n], p_ /; 2 Min[p] = = Max[p]], {n, z}](* A118096 *)
Table[Count[q[n], p_ /; 2 Min[p] > Max[p]], {n, z}] (* A053263 *)
Table[Count[q[n], p_ /; 2 Min[p] >= Max[p]], {n, z}] (* A237824 *)
A361858
Number of integer partitions of n such that the maximum is less than twice the median.
Original entry on oeis.org
1, 2, 3, 4, 5, 8, 8, 12, 15, 19, 22, 31, 34, 45, 55, 67, 78, 100, 115, 144, 170, 203, 238, 291, 337, 403, 473, 560, 650, 772, 889, 1046, 1213, 1414, 1635, 1906, 2186, 2533, 2913, 3361, 3847, 4433, 5060, 5808, 6628, 7572, 8615, 9835, 11158, 12698, 14394
Offset: 1
The a(1) = 1 through a(8) = 12 partitions:
(1) (2) (3) (4) (5) (6) (7) (8)
(11) (21) (22) (32) (33) (43) (44)
(111) (31) (41) (42) (52) (53)
(1111) (221) (51) (61) (62)
(11111) (222) (322) (71)
(321) (331) (332)
(2211) (2221) (431)
(111111) (1111111) (2222)
(3221)
(3311)
(22211)
(11111111)
The partition y = (3,2,2,1) has maximum 3 and median 2, and 3 < 2*2, so y is counted under a(8).
For minimum instead of median we have
A053263.
For length instead of median we have
A237754.
For mean instead of median we have
A361852.
A000975 counts subsets with integer median.
Cf.
A008284,
A027193,
A237751,
A237755,
A237820,
A237824,
A240219,
A361394,
A361851,
A361860,
A361907.
A361859
Number of integer partitions of n such that the maximum is greater than or equal to twice the median.
Original entry on oeis.org
0, 0, 0, 1, 2, 3, 7, 10, 15, 23, 34, 46, 67, 90, 121, 164, 219, 285, 375, 483, 622, 799, 1017, 1284, 1621, 2033, 2537, 3158, 3915, 4832, 5953, 7303, 8930, 10896, 13248, 16071, 19451, 23482, 28272, 33977, 40736, 48741, 58201, 69367, 82506, 97986, 116139
Offset: 1
The a(4) = 1 through a(9) = 15 partitions:
(211) (311) (411) (421) (422) (522)
(2111) (3111) (511) (521) (621)
(21111) (3211) (611) (711)
(4111) (4211) (4221)
(22111) (5111) (4311)
(31111) (32111) (5211)
(211111) (41111) (6111)
(221111) (33111)
(311111) (42111)
(2111111) (51111)
(321111)
(411111)
(2211111)
(3111111)
(21111111)
The partition y = (5,2,2,1) has maximum 5 and median 2, and 5 >= 2*2, so y is counted under a(10).
For length instead of median we have
A237752.
For minimum instead of median we have
A237821.
Reversing the inequality gives
A361848.
The complement is counted by
A361858.
These partitions have ranks
A361868.
For mean instead of median we have
A361906.
A000975 counts subsets with integer median.
Cf.
A008284,
A027193,
A067538,
A237755,
A237820,
A237824,
A240219,
A359907,
A361851,
A361860,
A361907.
A361908
Positive integers > 1 whose prime indices satisfy (maximum) = 2*(minimum).
Original entry on oeis.org
6, 12, 18, 21, 24, 36, 48, 54, 63, 65, 72, 96, 105, 108, 133, 144, 147, 162, 189, 192, 216, 288, 315, 319, 324, 325, 384, 432, 441, 455, 481, 486, 525, 567, 576, 648, 715, 731, 735, 768, 845, 864, 931, 945, 972, 1007, 1029, 1152, 1296, 1323, 1403, 1458, 1463
Offset: 1
The terms together with their prime indices begin:
6: {1,2}
12: {1,1,2}
18: {1,2,2}
21: {2,4}
24: {1,1,1,2}
36: {1,1,2,2}
48: {1,1,1,1,2}
54: {1,2,2,2}
63: {2,2,4}
65: {3,6}
72: {1,1,1,2,2}
96: {1,1,1,1,1,2}
The RHS is 2*
A055396 (twice minimum).
The LHS is
A061395 (greatest prime index).
Partitions of this type are counted by
A118096.
A001221 (omega) counts distinct prime factors.
A001222 (bigomega) counts prime factors with multiplicity.
-
filter:= proc(n) local F,b;
if n::even then b:= padic:-ordp(n,3);
if b = 0 then return false else return n = 2^padic:-ordp(n,2) * 3^b fi
fi;
F:= ifactors(n)[2][..,1];
nops(F) >= 2 and numtheory:-pi(max(F)) = 2*numtheory:-pi(min(F))
end proc:
select(filter, [$1..2000]); # Robert Israel, Mar 11 2025
-
Select[Range[2,100],PrimePi[FactorInteger[#][[-1,1]]]==2*PrimePi[FactorInteger[#][[1,1]]]&]
A361907
Number of integer partitions of n such that (length) * (maximum) > 2*n.
Original entry on oeis.org
0, 0, 0, 0, 0, 0, 3, 4, 7, 11, 19, 26, 43, 60, 80, 115, 171, 201, 297, 374, 485, 656, 853, 1064, 1343, 1758, 2218, 2673, 3477, 4218, 5423, 6523, 7962, 10017, 12104, 14409, 17978, 22031, 26318, 31453, 38176, 45442, 55137, 65775, 77451, 92533, 111485, 131057
Offset: 1
The a(7) = 3 through a(10) = 11 partitions:
(511) (611) (711) (721)
(4111) (5111) (5211) (811)
(31111) (41111) (6111) (6211)
(311111) (42111) (7111)
(51111) (52111)
(411111) (61111)
(3111111) (421111)
(511111)
(3211111)
(4111111)
(31111111)
The partition y = (3,2,1,1) has length 4 and maximum 3, and 4*3 is not > 2*7, so y is not counted under a(7).
The partition y = (4,2,1,1) has length 4 and maximum 4, and 4*4 is not > 2*8, so y is not counted under a(8).
The partition y = (5,1,1,1) has length 4 and maximum 5, and 4*5 > 2*8, so y is counted under a(8).
The partition y = (5,2,1,1) has length 4 and maximum 5, and 4*5 > 2*9, so y is counted under a(9).
The partition y = (3,2,1,1) has diagram:
o o o
o o .
o . .
o . .
with complement (shown in dots) of size 5, and 5 is not > 7, so y is not counted under a(7).
Reversing the inequality gives
A361852.
A051293 counts subsets with integer mean.
A116608 counts partitions by number of distinct parts.
Cf.
A027193,
A111907,
A237752,
A237755,
A237821,
A237824,
A237984,
A324562,
A326622,
A327482,
A349156,
A360071,
A361394.
A361857
Number of integer partitions of n such that the maximum is greater than twice the median.
Original entry on oeis.org
0, 0, 0, 0, 1, 2, 3, 7, 11, 16, 25, 37, 52, 74, 101, 138, 185, 248, 325, 428, 554, 713, 914, 1167, 1476, 1865, 2336, 2922, 3633, 4508, 5562, 6854, 8405, 10284, 12536, 15253, 18489, 22376, 26994, 32507, 39038, 46802, 55963, 66817, 79582, 94643, 112315
Offset: 1
The a(5) = 1 through a(10) = 16 partitions:
(311) (411) (511) (521) (522) (622)
(3111) (4111) (611) (621) (721)
(31111) (4211) (711) (811)
(5111) (5211) (5221)
(32111) (6111) (5311)
(41111) (33111) (6211)
(311111) (42111) (7111)
(51111) (43111)
(321111) (52111)
(411111) (61111)
(3111111) (331111)
(421111)
(511111)
(3211111)
(4111111)
(31111111)
The partition y = (5,2,2,1) has maximum 5 and median 2, and 5 > 2*2, so y is counted under a(10).
For length instead of median we have
A237751.
For minimum instead of median we have
A237820.
The complement is counted by
A361848.
Reversing the inequality gives
A361858.
These partitions have ranks
A361867.
For mean instead of median we have
A361907.
A000975 counts subsets with integer median.
A361867
Positive integers > 1 whose prime indices satisfy (maximum) > 2*(median).
Original entry on oeis.org
20, 28, 40, 44, 52, 56, 66, 68, 76, 78, 80, 84, 88, 92, 99, 102, 104, 112, 114, 116, 117, 120, 124, 132, 136, 138, 148, 152, 153, 156, 160, 164, 168, 170, 171, 172, 174, 176, 184, 186, 188, 190, 198, 200, 204, 207, 208, 212, 220, 222, 224, 228, 230, 232, 234
Offset: 1
The prime indices of 84 are {1,1,2,4}, with maximum 4 and median 3/2, and 4 > 2*(3/2), so 84 is in the sequence.
The terms together with their prime indices begin:
20: {1,1,3}
28: {1,1,4}
40: {1,1,1,3}
44: {1,1,5}
52: {1,1,6}
56: {1,1,1,4}
66: {1,2,5}
68: {1,1,7}
76: {1,1,8}
78: {1,2,6}
80: {1,1,1,1,3}
84: {1,1,2,4}
88: {1,1,1,5}
92: {1,1,9}
99: {2,2,5}
The LHS is
A061395 (greatest prime index).
For mean instead of median we have
A361907.
A000975 counts subsets with integer median.
-
prix[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n], {p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[100], Max@@prix[#]>2*Median[prix[#]]&]
A361909
Positive integers > 1 whose prime indices satisfy: (maximum) = 2*(length).
Original entry on oeis.org
3, 14, 21, 35, 49, 52, 78, 117, 130, 152, 182, 195, 228, 273, 286, 325, 338, 342, 380, 429, 455, 464, 507, 513, 532, 570, 637, 696, 715, 798, 836, 845, 855, 950, 988, 1001, 1044, 1160, 1183, 1184, 1197, 1254, 1292, 1330, 1425, 1444, 1482, 1566, 1573, 1624
Offset: 1
The terms together with their prime indices begin:
3: {2}
14: {1,4}
21: {2,4}
35: {3,4}
49: {4,4}
52: {1,1,6}
78: {1,2,6}
117: {2,2,6}
130: {1,3,6}
152: {1,1,1,8}
182: {1,4,6}
195: {2,3,6}
228: {1,1,2,8}
273: {2,4,6}
286: {1,5,6}
325: {3,3,6}
338: {1,6,6}
342: {1,2,2,8}
Without multiplying by 2 in the RHS, we have
A106529.
Partitions of this type are counted by
A237753.
The RHS is
A255201 (twice bigomega).
A001221 (omega) counts distinct prime factors.
A001222 (bigomega) counts prime factors with multiplicity.
A362981
Heinz numbers of integer partitions such that 2*(least part) >= greatest part.
Original entry on oeis.org
1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 15, 16, 17, 18, 19, 21, 23, 24, 25, 27, 29, 31, 32, 35, 36, 37, 41, 43, 45, 47, 48, 49, 53, 54, 55, 59, 61, 63, 64, 65, 67, 71, 72, 73, 75, 77, 79, 81, 83, 89, 91, 96, 97, 101, 103, 105, 107, 108, 109, 113, 119, 121, 125
Offset: 1
The terms together with their prime indices begin:
1: {} 16: {1,1,1,1} 36: {1,1,2,2}
2: {1} 17: {7} 37: {12}
3: {2} 18: {1,2,2} 41: {13}
4: {1,1} 19: {8} 43: {14}
5: {3} 21: {2,4} 45: {2,2,3}
6: {1,2} 23: {9} 47: {15}
7: {4} 24: {1,1,1,2} 48: {1,1,1,1,2}
8: {1,1,1} 25: {3,3} 49: {4,4}
9: {2,2} 27: {2,2,2} 53: {16}
11: {5} 29: {10} 54: {1,2,2,2}
12: {1,1,2} 31: {11} 55: {3,5}
13: {6} 32: {1,1,1,1,1} 59: {17}
15: {2,3} 35: {3,4} 61: {18}
For prime factors instead of indices we have
A081306.
Partitions of this type are counted by
A237824.
-
prix[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[100],2*Min@@prix[#]>=Max@@prix[#]&]
Showing 1-10 of 11 results.
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