A360007
Positions of first appearances in the sequence giving the median of the prime indices of n (A360005(n)/2).
Original entry on oeis.org
1, 2, 3, 5, 6, 7, 11, 13, 14, 17, 19, 23, 26, 29, 31, 37, 38, 41, 43, 47, 53, 58, 59, 61, 67, 71, 73, 74, 79, 83, 86, 89, 97, 101, 103, 106, 107, 109, 113, 122, 127, 131, 137, 139, 142, 149, 151, 157, 158, 163, 167, 173, 178, 179, 181, 191, 193, 197, 199, 202
Offset: 1
Positions of first appearances in
A360005.
For mean instead of median we have
A360008.
A316413 lists numbers whose prime indices have integer mean.
A359908 = numbers w/ integer median of prime indices, complement
A359912.
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nn=1000;
prix[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
seq=Table[If[n==1,1,2*Median[prix[n]]],{n,nn}];
Select[Range[nn],FreeQ[seq[[Range[#-1]]],seq[[#]]]&]
A359893
Triangle read by rows where T(n,k) is the number of integer partitions of n with median k, where k ranges from 1 to n in steps of 1/2.
Original entry on oeis.org
1, 1, 0, 1, 1, 1, 0, 0, 1, 2, 0, 2, 0, 0, 0, 1, 3, 0, 1, 2, 0, 0, 0, 0, 1, 4, 1, 2, 0, 3, 0, 0, 0, 0, 0, 1, 6, 1, 3, 0, 1, 3, 0, 0, 0, 0, 0, 0, 1, 8, 1, 6, 0, 2, 0, 4, 0, 0, 0, 0, 0, 0, 0, 1, 11, 2, 7, 1, 3, 0, 1, 4, 0, 0, 0, 0, 0, 0, 0, 0, 1
Offset: 1
Triangle begins:
1
1 0 1
1 1 0 0 1
2 0 2 0 0 0 1
3 0 1 2 0 0 0 0 1
4 1 2 0 3 0 0 0 0 0 1
6 1 3 0 1 3 0 0 0 0 0 0 1
8 1 6 0 2 0 4 0 0 0 0 0 0 0 1
11 2 7 1 3 0 1 4 0 0 0 0 0 0 0 0 1
15 2 10 3 4 0 2 0 5 0 0 0 0 0 0 0 0 0 1
20 3 13 3 7 0 3 0 1 5 0 0 0 0 0 0 0 0 0 0 1
26 4 19 3 11 1 4 0 2 0 6 0 0 0 0 0 0 0 0 0 0 0 1
For example, row n = 8 counts the following partitions:
611 4211 422 . 332 . 44 . . . . . . . 8
5111 521 431 53
32111 2222 62
41111 3221 71
221111 3311
311111 22211
2111111
11111111
Row lengths are 2n-1 =
A005408(n-1).
The median statistic is ranked by
A360005(n)/2.
A240219 counts partitions w/ the same mean as median, complement
A359894.
-
Table[Length[Select[IntegerPartitions[n], Median[#]==k&]],{n,1,10},{k,1,n,1/2}]
A359901
Triangle read by rows where T(n,k) is the number of integer partitions of n with median k = 1..n.
Original entry on oeis.org
1, 1, 1, 1, 0, 1, 2, 2, 0, 1, 3, 1, 0, 0, 1, 4, 2, 3, 0, 0, 1, 6, 3, 1, 0, 0, 0, 1, 8, 6, 2, 4, 0, 0, 0, 1, 11, 7, 3, 1, 0, 0, 0, 0, 1, 15, 10, 4, 2, 5, 0, 0, 0, 0, 1, 20, 13, 7, 3, 1, 0, 0, 0, 0, 0, 1, 26, 19, 11, 4, 2, 6, 0, 0, 0, 0, 0, 1
Offset: 1
Triangle begins:
1
1 1
1 0 1
2 2 0 1
3 1 0 0 1
4 2 3 0 0 1
6 3 1 0 0 0 1
8 6 2 4 0 0 0 1
11 7 3 1 0 0 0 0 1
15 10 4 2 5 0 0 0 0 1
20 13 7 3 1 0 0 0 0 0 1
26 19 11 4 2 6 0 0 0 0 0 1
35 24 14 5 3 1 0 0 0 0 0 0 1
45 34 17 8 4 2 7 0 0 0 0 0 0 1
58 42 23 12 5 3 1 0 0 0 0 0 0 0 1
For example, row n = 9 counts the following partitions:
(7,1,1) (5,2,2) (3,3,3) (4,4,1) . . . . (9)
(6,1,1,1) (6,2,1) (4,3,2)
(3,3,1,1,1) (3,2,2,2) (5,3,1)
(4,2,1,1,1) (4,2,2,1)
(5,1,1,1,1) (4,3,1,1)
(3,2,1,1,1,1) (2,2,2,2,1)
(4,1,1,1,1,1) (3,2,2,1,1)
(2,2,1,1,1,1,1)
(3,1,1,1,1,1,1)
(2,1,1,1,1,1,1,1)
(1,1,1,1,1,1,1,1,1)
Including half-steps gives
A359893.
The median statistic is ranked by
A360005(n)/2.
A240219 counts partitions w/ the same mean as median, complement
A359894.
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Table[Length[Select[IntegerPartitions[n],Median[#]==k&]],{n,15},{k,n}]
A359908
Numbers whose prime indices have integer median.
Original entry on oeis.org
2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 27, 28, 29, 30, 31, 32, 34, 37, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 52, 53, 54, 55, 56, 57, 59, 61, 62, 63, 64, 66, 67, 68, 70, 71, 72, 73, 75, 76, 78, 79, 80, 81, 82, 83
Offset: 1
The prime indices of 180 are {1,1,2,2,3}, with median 2, so 180 is in the sequence.
The prime indices of 360 are {1,1,1,2,2,3}, with median 3/2, so 360 is not in the sequence.
For mean instead of median we have
A316413.
The median of prime indices is given by
A360005/2.
The case of integer mean also is
A360009.
-
prix[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[100],IntegerQ[Median[prix[#]]]&]
A359902
Triangle read by rows where T(n,k) is the number of odd-length integer partitions of n with median k.
Original entry on oeis.org
1, 0, 1, 1, 0, 1, 1, 0, 0, 1, 2, 1, 0, 0, 1, 2, 2, 0, 0, 0, 1, 4, 2, 1, 0, 0, 0, 1, 4, 3, 2, 0, 0, 0, 0, 1, 7, 4, 3, 1, 0, 0, 0, 0, 1, 8, 6, 3, 2, 0, 0, 0, 0, 0, 1, 12, 8, 4, 3, 1, 0, 0, 0, 0, 0, 1, 14, 11, 5, 4, 2, 0, 0, 0, 0, 0, 0, 1
Offset: 1
Triangle begins:
1
0 1
1 0 1
1 0 0 1
2 1 0 0 1
2 2 0 0 0 1
4 2 1 0 0 0 1
4 3 2 0 0 0 0 1
7 4 3 1 0 0 0 0 1
8 6 3 2 0 0 0 0 0 1
12 8 4 3 1 0 0 0 0 0 1
14 11 5 4 2 0 0 0 0 0 0 1
21 14 8 4 3 1 0 0 0 0 0 0 1
24 20 10 5 4 2 0 0 0 0 0 0 0 1
34 25 15 6 5 3 1 0 0 0 0 0 0 0 1
For example, row n = 9 counts the following partitions:
(7,1,1) (5,2,2) (3,3,3) (4,4,1) . . . . (9)
(3,3,1,1,1) (6,2,1) (4,3,2)
(4,2,1,1,1) (2,2,2,2,1) (5,3,1)
(5,1,1,1,1) (3,2,2,1,1)
(2,2,1,1,1,1,1)
(3,1,1,1,1,1,1)
(1,1,1,1,1,1,1,1,1)
The median statistic is ranked by
A360005(n)/2.
A240219 counts partitions w/ the same mean as median, complement
A359894.
-
Table[Length[Select[IntegerPartitions[n],OddQ[Length[#]]&&Median[#]==k&]],{n,15},{k,n}]
A307683
Number of partitions of n having a non-integer median.
Original entry on oeis.org
0, 0, 1, 0, 2, 1, 4, 1, 7, 5, 11, 8, 18, 17, 31, 28, 47, 51, 75, 81, 119, 134, 181, 206, 277, 323, 420, 488, 623, 737, 922, 1084, 1352, 1597, 1960, 2313, 2819, 3330, 4029, 4743, 5704, 6722, 8030, 9434, 11234, 13175, 15601, 18262, 21552, 25184, 29612, 34518
Offset: 1
a(7) counts these 4 partitions: [6,1], [5,2], [4,3], [3,2,1,1].
Cf.
A000016,
A051293,
A067538,
A082550,
A240219,
A240850,
A316413,
A326567/
A326568,
A327475,
A359897,
A360005.
A359907
Number of strict integer partitions of n with integer median.
Original entry on oeis.org
0, 1, 1, 1, 2, 1, 4, 2, 6, 4, 9, 6, 14, 10, 18, 16, 27, 23, 36, 34, 51, 49, 67, 68, 94, 95, 122, 129, 166, 174, 217, 233, 287, 308, 371, 405, 487, 528, 622, 683, 805, 880, 1024, 1127, 1305, 1435, 1648, 1818, 2086, 2295, 2611, 2882, 3273, 3606, 4076, 4496, 5069
Offset: 0
The a(1) = 1 through a(14) = 18 partitions (A..E = 10..14):
1 2 3 4 5 6 7 8 9 A B C D E
31 42 421 53 432 64 542 75 643 86
51 62 531 73 632 84 652 95
321 71 621 82 641 93 742 A4
431 91 731 A2 751 B3
521 532 821 B1 832 C2
541 543 841 D1
631 642 931 653
721 651 A21 743
732 6421 752
741 761
831 842
921 851
5421 932
941
A31
B21
7421
The median statistic is ranked by
A360005(n)/2.
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Table[Length[Select[IntegerPartitions[n],UnsameQ@@#&&IntegerQ[Median[#]]&]],{n,0,30}]
A359889
Numbers that are 1 or whose prime indices have the same mean as median.
Original entry on oeis.org
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 19, 21, 22, 23, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 41, 43, 46, 47, 49, 51, 53, 55, 57, 58, 59, 61, 62, 64, 65, 67, 69, 71, 73, 74, 77, 79, 81, 82, 83, 85, 86, 87, 89, 90, 91, 93, 94
Offset: 1
The prime indices of 900 are {1,1,2,2,3,3}, with mean 2 and median 2, so 900 is in the sequence.
The RHS (median of prime indices) is
A360005/2.
A316413 lists numbers whose prime indices have integer mean.
A359908 lists numbers whose prime indices have integer median.
-
prix[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[100],#==1||Mean[prix[#]]==Median[prix[#]]&]
A063655
Smallest semiperimeter of integral rectangle with area n.
Original entry on oeis.org
2, 3, 4, 4, 6, 5, 8, 6, 6, 7, 12, 7, 14, 9, 8, 8, 18, 9, 20, 9, 10, 13, 24, 10, 10, 15, 12, 11, 30, 11, 32, 12, 14, 19, 12, 12, 38, 21, 16, 13, 42, 13, 44, 15, 14, 25, 48, 14, 14, 15, 20, 17, 54, 15, 16, 15, 22, 31, 60, 16, 62, 33, 16, 16, 18, 17, 68, 21, 26
Offset: 1
Since 15 = 1*15 = 3*5 and the 3*5 rectangle gives smallest semiperimeter 8, we have a(15)=8.
Positions of odd terms are
A139710.
Positions of even terms are
A139711.
A000975 counts subsets with integer median.
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A063655 := proc(n)
local i,j;
for i from floor(sqrt(n)) to 1 by -1 do
j := floor(n/i) ;
if i*j = n then
return i+j;
end if;
end do:
end proc:
seq(A063655(n), n=1..80); # Winston C. Yang, Feb 03 2002
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Table[d = Divisors[n]; len = Length[d]; If[OddQ[len], 2*Sqrt[n], d[[len/2]] + d[[1 + len/2]]], {n, 100}] (* T. D. Noe, Mar 06 2012 *)
Table[2*Median[Divisors[n]],{n,100}] (* Gus Wiseman, Mar 18 2023 *)
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A063655(n) = { my(c=1); fordiv(n,d,if((d*d)>=n,if((d*d)==n,return(2*d),return(c+d))); c=d); (0); }; \\ Antti Karttunen, Oct 20 2017
-
from sympy import divisors
def A063655(n):
d = divisors(n)
l = len(d)
return d[(l-1)//2] + d[l//2] # Chai Wah Wu, Jun 14 2019
Corrected and extended by Larry Reeves (larryr(AT)acm.org) and
Dean Hickerson, Jul 26 2001
A360457
Two times the median of the set of distinct prime indices of n; a(1) = 1.
Original entry on oeis.org
1, 2, 4, 2, 6, 3, 8, 2, 4, 4, 10, 3, 12, 5, 5, 2, 14, 3, 16, 4, 6, 6, 18, 3, 6, 7, 4, 5, 20, 4, 22, 2, 7, 8, 7, 3, 24, 9, 8, 4, 26, 4, 28, 6, 5, 10, 30, 3, 8, 4, 9, 7, 32, 3, 8, 5, 10, 11, 34, 4, 36, 12, 6, 2, 9, 4, 38, 8, 11, 6, 40, 3, 42, 13, 5, 9, 9, 4, 44, 4
Offset: 1
The prime indices of 65 are {3,6}, with distinct parts {3,6}, with median 9/2, so a(65) = 9.
The prime indices of 900 are {1,1,2,2,3,3}, with distinct parts {1,2,3}, with median 2, so a(900) = 4.
The version for divisors is
A063655.
The version for all prime indices is
A360005.
The version for distinct prime factors is
A360458.
The version for all prime factors is
A360459.
The version for prime multiplicities is
A360460.
Positions of even terms are
A360550.
Positions of odd terms are
A360551.
The version for 0-prepended differences is
A360555.
A304038 lists distinct prime indices.
-
Table[If[n==1,1,2*Median[PrimePi/@First/@FactorInteger[n]]],{n,100}]
Showing 1-10 of 116 results.
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