A367912
Number of multisets that can be obtained by choosing a binary index of each binary index of n.
Original entry on oeis.org
1, 1, 1, 1, 2, 2, 2, 2, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 4, 4, 4, 4, 2, 2, 2, 2, 4, 4, 4, 4, 2, 2, 2, 2, 4, 4, 4, 4, 2, 2, 2, 2, 4, 4, 4, 4, 4, 4, 4, 4, 7, 7, 7, 7, 4, 4, 4, 4, 7, 7, 7, 7, 3, 3, 3, 3, 5, 5, 5, 5, 3, 3, 3, 3, 5, 5, 5, 5, 5, 5, 5, 5, 8, 8, 8, 8
Offset: 0
The binary indices of binary indices of 52 are {{1,2},{1,3},{2,3}}, with multiset choices {1,1,2}, {1,1,3}, {1,2,2}, {1,2,3}, {1,3,3}, {2,2,3}, {2,3,3}, so a(52) = 7.
The version for multisets and divisors is
A355733, for sequences
A355731.
Choosing a sequence instead of multiset gives
A368109, firsts
A368111.
A070939 gives length of binary expansion.
A096111 gives product of binary indices.
Cf.
A072639,
A309326,
A326031,
A326702,
A326753,
A355735,
A355739,
A355740,
A355745,
A367771,
A367906.
-
bpe[n_]:=Join@@Position[Reverse[IntegerDigits[n, 2]],1];
Table[Length[Union[Sort/@Tuples[bpe/@bpe[n]]]], {n,0,100}]
A370802
Positive integers with as many prime factors (A001222) as distinct divisors of prime indices (A370820).
Original entry on oeis.org
1, 2, 6, 9, 10, 22, 25, 28, 30, 34, 42, 45, 62, 63, 66, 75, 82, 92, 98, 99, 102, 104, 110, 118, 121, 134, 140, 147, 152, 153, 156, 166, 170, 186, 210, 218, 228, 230, 232, 234, 246, 254, 260, 275, 276, 279, 289, 308, 310, 314, 315, 330, 342, 343, 344, 348, 350
Offset: 1
The prime indices of 1617 are {2,4,4,5}, with distinct divisors {1,2,4,5}, so 1617 is in the sequence.
The terms together with their prime indices begin:
1: {}
2: {1}
6: {1,2}
9: {2,2}
10: {1,3}
22: {1,5}
25: {3,3}
28: {1,1,4}
30: {1,2,3}
34: {1,7}
42: {1,2,4}
45: {2,2,3}
62: {1,11}
63: {2,2,4}
66: {1,2,5}
75: {2,3,3}
82: {1,13}
92: {1,1,9}
98: {1,4,4}
99: {2,2,5}
102: {1,2,7}
104: {1,1,1,6}
For factors instead of divisors on the RHS we have
A319899.
A version for binary indices is
A367917.
For (greater than) instead of (equal) we have
A370348, counted by
A371171.
For divisors instead of factors on LHS we have
A371165, counted by
A371172.
For only distinct prime factors on LHS we have
A371177, counted by
A371178.
A001221 counts distinct prime factors.
A355731 counts choices of a divisor of each prime index, firsts
A355732.
Cf.
A000792,
A003963,
A355529,
A355737,
A355739,
A355741,
A368100,
A370808,
A370813,
A370814,
A371127.
-
Select[Range[100],PrimeOmega[#]==Length[Union @@ Divisors/@PrimePi/@First/@If[#==1,{},FactorInteger[#]]]&]
A370348
Numbers k such that there are fewer divisors of prime indices of k than there are prime indices of k.
Original entry on oeis.org
4, 8, 12, 16, 18, 20, 24, 27, 32, 36, 40, 44, 48, 50, 54, 56, 60, 64, 68, 72, 80, 81, 84, 88, 90, 96, 100, 108, 112, 120, 124, 125, 126, 128, 132, 135, 136, 144, 150, 160, 162, 164, 168, 176, 180, 184, 189, 192, 196, 198, 200, 204, 208, 216, 220, 224, 225, 236, 240, 242, 243, 248, 250, 252, 256
Offset: 1
a(5) = 18 is a term because the prime indices of 18 = 2 * 3^2 are 1,2,2, and there are 3 of these but only 2 divisors of prime indices, namely 1 and 2.
For submultisets instead of parts on the RHS we get
A371167.
Partitions of this type are counted by
A371171.
A001221 counts distinct prime factors.
A355731 counts choices of a divisor of each prime index, firsts
A355732.
-
filter:= proc(n) uses numtheory; local F,D,t;
F:= map(t -> [pi(t[1]),t[2]], ifactors(n)[2]);
D:= `union`(seq(divisors(t[1]), t = F));
nops(D) < add(t[2], t = F)
end proc:
select(filter, [$1..300]);
-
filter[n_] := Module[{F, d},
F = {PrimePi[#[[1]]], #[[2]]}& /@ FactorInteger[n];
d = Union[Flatten[Divisors /@ F[[All, 1]]]];
Length[d] < Total[F[[All, 2]]]];
Select[Range[300], filter] (* Jean-François Alcover, Mar 08 2024, after Maple code *)
A370803
Number of integer partitions of n such that more than one set can be obtained by choosing a different divisor of each part.
Original entry on oeis.org
0, 0, 1, 1, 1, 3, 2, 4, 5, 7, 10, 11, 15, 18, 25, 28, 39, 45, 59, 66, 83, 101, 123, 150, 176, 213, 252, 301, 352, 426, 497, 589, 684, 802, 939, 1095, 1270, 1480, 1718, 1985, 2289, 2645, 3056, 3489, 4019, 4590, 5289, 6014, 6877, 7817, 8955, 10134, 11551, 13085
Offset: 0
The partition (6,4,4,1) has two choices, namely {1,2,4,6} and {1,2,3,4}, so is counted under a(15).
The a(0) = 0 through a(13) = 18 partitions (A..D = 10..13):
. . 2 3 4 5 6 7 8 9 A B C D
32 42 43 44 54 64 65 66 76
41 52 53 63 73 74 75 85
61 62 72 82 83 84 94
431 81 91 92 93 A3
432 433 A1 A2 B2
621 532 443 543 C1
541 542 633 544
622 632 642 643
631 641 651 652
821 732 661
741 742
822 832
831 841
921 922
A21
5431
6421
Including partitions with one choice gives
A239312, complement
A370320.
These partitions have ranks
A370811.
A355731 counts choices of a divisor of each prime index, firsts
A355732.
A355733 counts divisor-choices of prime indices.
-
Table[Length[Select[IntegerPartitions[n],Length[Union[Sort /@ Select[Tuples[Divisors/@#],UnsameQ@@#&]]]>1&]],{n,0,30}]
A371130
Number of integer partitions of n such that the number of parts is equal to the number of distinct divisors of parts.
Original entry on oeis.org
1, 1, 0, 1, 2, 0, 4, 2, 4, 5, 5, 11, 10, 16, 17, 21, 26, 32, 44, 53, 69, 71, 101, 110, 148, 168, 205, 249, 289, 356, 418, 502, 589, 716, 812, 999, 1137, 1365, 1566, 1873, 2158, 2537, 2942, 3449, 4001, 4613, 5380, 6193, 7220, 8224, 9575, 10926, 12683, 14430
Offset: 0
The partition (6,2,2,1) has 4 parts and 4 distinct divisors of parts {1,2,3,6} so is counted under a(11).
The a(1) = 1 through a(11) = 11 partitions:
(1) . (21) (22) . (33) (322) (71) (441) (55) (533)
(31) (51) (421) (332) (522) (442) (722)
(321) (422) (531) (721) (731)
(411) (521) (4311) (4321) (911)
(6111) (6211) (4322)
(4331)
(5321)
(5411)
(6221)
(6311)
(8111)
These partitions are ranked by
A370802.
For (greater than) instead of (equal to) we have
A371171, ranks
A370348.
For submultisets instead of parts on the LHS we have
A371172.
For (less than) instead of (equal to) we have
A371173, ranked by
A371168.
A008284 counts partitions by length.
-
Table[Length[Select[IntegerPartitions[n], Length[#]==Length[Union@@Divisors/@#]&]],{n,0,30}]
A381715
Number of multisets that can be obtained by taking the sum of each block of a multiset partition of the prime indices of n into distinct constant blocks.
Original entry on oeis.org
1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 1, 1, 1, 4, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 1, 1
Offset: 1
The prime indices of 1728 are {1,1,1,1,1,1,2,2,2}, with multiset partitions into distinct constant blocks:
{{2,2,2},{1,1,1,1,1,1}}
{{1},{2,2,2},{1,1,1,1,1}}
{{2},{2,2},{1,1,1,1,1,1}}
{{1,1},{2,2,2},{1,1,1,1}}
{{1},{2},{2,2},{1,1,1,1,1}}
{{1},{1,1},{1,1,1},{2,2,2}}
{{2},{1,1},{2,2},{1,1,1,1}}
{{1},{2},{1,1},{2,2},{1,1,1}}
with sums:
{6,6}
{1,5,6}
{2,4,6}
{2,4,6}
{1,2,4,5}
{1,2,3,6}
{2,2,4,4}
{1,2,2,3,4}
of which 7 are distinct, so a(1728) = 7.
Positions of terms > 1 are
A046099.
For equal instead of distinct blocks we have
A362421.
For strict instead of constant blocks we have
A381441, before sums
A050326.
A003963 gives product of prime indices.
Cf.
A000720,
A001222,
A002846,
A005117,
A050342,
A213242,
A213385,
A293511,
A299202,
A300385,
A317142,
A381870.
-
prix[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
sps[{}]:={{}};sps[set:{i_,_}]:=Join@@Function[s,Prepend[#,s]&/@sps[Complement[set,s]]]/@Cases[Subsets[set],{i,_}];
mps[mset_]:=Union[Sort[Sort/@(#/.x_Integer:>mset[[x]])]&/@sps[Range[Length[mset]]]];
Table[Length[Union[Sort[Total/@#]&/@Select[mps[prix[n]],UnsameQ@@#&&And@@SameQ@@@#&]]],{n,100}]
A355735
Number of ways to choose a divisor of each prime index of n (taken in weakly increasing order) such that the result is weakly increasing.
Original entry on oeis.org
1, 1, 2, 1, 2, 2, 3, 1, 3, 2, 2, 2, 4, 3, 3, 1, 2, 3, 4, 2, 5, 2, 3, 2, 3, 4, 4, 3, 4, 3, 2, 1, 3, 2, 4, 3, 6, 4, 7, 2, 2, 5, 4, 2, 4, 3, 4, 2, 6, 3, 3, 4, 5, 4, 3, 3, 7, 4, 2, 3, 6, 2, 7, 1, 6, 3, 2, 2, 5, 4, 6, 3, 4, 6, 4, 4, 4, 7, 4, 2, 5, 2, 2, 5, 3, 4, 7
Offset: 1
The a(15) = 3 ways are: (1,1), (1,3), (2,3).
The a(18) = 3 ways are: (1,1,1), (1,1,2), (1,2,2).
The a(2) = 1 through a(19) = 4 ways:
1 1 11 1 11 1 111 11 11 1 111 1 11 11 1111 1 111 1
2 3 12 2 12 13 5 112 2 12 13 7 112 2
4 22 3 14 23 122 4
6 8
Choosing a multiset instead of sequence gives
A355733, firsts
A355734.
Positions of first appearances are
A355736.
A003963 multiplies together the prime indices of n.
A061395 selects the maximum prime index.
A120383 lists numbers divisible by all of their prime indices.
A324850 lists numbers divisible by the product of their prime indices.
Cf.
A000720,
A076610,
A316524,
A335433,
A335448,
A340827,
A340852,
A344616,
A355737,
A355739,
A355740,
A355742.
-
primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Table[Length[Select[Tuples[Divisors/@primeMS[n]],LessEqual@@#&]],{n,100}]
A355734
Least k such that there are exactly n multisets that can be obtained by choosing a divisor of each prime index of k.
Original entry on oeis.org
1, 3, 7, 13, 21, 35, 39, 89, 133, 105, 91, 195, 351, 285, 247, 333, 273, 481, 455, 555, 623, 801, 791, 741, 1359, 1157, 1281, 1335, 1365, 1443, 1977, 1729, 1967, 1869, 2109, 3185, 2373, 2769, 2639, 4361, 3367, 3653, 3885, 3471, 4613, 5883, 5187, 5551, 6327
Offset: 1
The terms together with their prime indices begin:
1: {}
3: {2}
7: {4}
13: {6}
21: {2,4}
35: {3,4}
39: {2,6}
89: {24}
133: {4,8}
105: {2,3,4}
91: {4,6}
195: {2,3,6}
351: {2,2,2,6}
For example, the choices for a(12) = 195 are:
{1,1,1} {1,2,2} {1,3,6}
{1,1,2} {1,2,3} {2,2,3}
{1,1,3} {1,2,6} {2,3,3}
{1,1,6} {1,3,3} {2,3,6}
Positions of first appearances in
A355733.
A003963 multiplies together the prime indices of n.
A120383 lists numbers divisible by all of their prime indices.
A324850 lists numbers divisible by the product of their prime indices.
-
primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
mnrm[s_]:=If[Min@@s==1,mnrm[DeleteCases[s-1,0]]+1,0];
az=Table[Length[Union[Sort/@Tuples[Divisors/@primeMS[n]]]],{n,1000}];
Table[Position[az,k][[1,1]],{k,mnrm[az]}]
A371171
Number of integer partitions of n with more parts than distinct divisors of parts.
Original entry on oeis.org
0, 0, 1, 1, 2, 4, 5, 9, 12, 18, 26, 34, 50, 65, 92, 121, 161, 209, 274, 353, 456, 590, 745, 950, 1195, 1507, 1885, 2350, 2923, 3611, 4465, 5485, 6735, 8223, 10050, 12195, 14822, 17909, 21653, 26047, 31340, 37557, 44990, 53708, 64068, 76241, 90583, 107418
Offset: 1
The partition (3,2,1,1) has 4 parts {1,2,3,4} and 3 distinct divisors of parts {1,2,3}, so is counted under a(7).
The a(0) = 0 through a(8) = 12 partitions:
. . (11) (111) (211) (221) (222) (331) (2222)
(1111) (311) (2211) (511) (3221)
(2111) (3111) (2221) (3311)
(11111) (21111) (3211) (4211)
(111111) (4111) (5111)
(22111) (22211)
(31111) (32111)
(211111) (41111)
(1111111) (221111)
(311111)
(2111111)
(11111111)
The partitions are ranked by
A370348.
For submultisets instead of parts on the LHS we get ranks
A371167.
-
Table[Length[Select[IntegerPartitions[n],Length[#] > Length[Union@@Divisors/@#]&]],{n,0,30}]
A355535
Odd numbers of which it is not possible to choose a different prime factor of each prime index.
Original entry on oeis.org
9, 21, 25, 27, 45, 49, 57, 63, 75, 81, 99, 105, 115, 117, 121, 125, 133, 135, 147, 153, 159, 171, 175, 189, 195, 207, 225, 231, 243, 245, 261, 273, 275, 279, 285, 289, 297, 315, 325, 333, 343, 345, 351, 357, 361, 363, 369, 371, 375, 387, 393, 399, 405, 423
Offset: 1
The terms together with their prime indices begin:
9: {2,2}
21: {2,4}
25: {3,3}
27: {2,2,2}
45: {2,2,3}
49: {4,4}
57: {2,8}
63: {2,2,4}
75: {2,3,3}
81: {2,2,2,2}
99: {2,2,5}
105: {2,3,4}
For example, the prime indices of 897 are {2,6,9}, of which we can choose prime factors in two ways: (2,2,3) or (2,3,3); but neither of these has all distinct elements, so 897 is in the sequence.
The version for all divisors including evens is
A355740, zeros of
A355739.
Choices of a prime factor of each prime index:
A355741, unordered
A355744.
A001222 counts prime factors with multiplicity.
A003963 multiplies together the prime indices of n.
A120383 lists numbers divisible by all of their prime indices.
-
primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[100],OddQ[#]&&Select[Tuples[primeMS/@primeMS[#]],UnsameQ@@#&]=={}&]
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