cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-4 of 4 results.

A275472 First differences of A275316.

Original entry on oeis.org

945, 1575, 2520, 1008, 4500, 2640, 4416, 49104, 2160, 432, 9072, 5616, 28080, 10440, 8280, 16380, 8100, 18576, 4464, 15840, 5184, 123228, 26460, 25704, 3024, 68400, 31203, 31293, 15264, 110880, 12960, 0, 9720, 16200, 51840, 35640, 71880, 57288, 49032, 81000
Offset: 1

Views

Author

Timothy L. Tiffin, Jul 29 2016

Keywords

Comments

The terms represent differences between consecutive amicable pair averages given in A275316.
Interestingly, the first two odd abundant numbers begin this sequence: a(1) = 945 = A005231(1) and a(2) = 1575 = A005231(2).
Of the first 141 terms, 4 are odd, 137 are even, 136 are abundant, 2 are deficient [specifically, a(27) = 31203 and a(28) = 31293], 7 numbers occur twice [specifically, a(53) = a(59) = 1728, a(25) = a(136) = 3024, a(21) = a(127) = 5184, a(31) = a(137) = 12960, a(34) = a(41) = 16200, a(74) = a(77) = 20736, and a(66) = a(104) = 156240], 3 numbers occur three times [specifically, a(32) = a(107) = a(139) = 0, a(35) = a(42) = a(52) = 51840, and a(30) = a(86) = a(97) = 110880], and every number is divisible by 3.
a(n) = A275066(n) for 41 of the first 141 indices: n = 1, 2, 3, 4, 5, 6, 7, 12, 13, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 36, 37, 38, 39, 43, 44, 48, 49, 50, 57, 58, 59, 64, 65, 95, 120, 121.
a(n) = -A275066(n) for 9 of the first 141 indices: n = 15, 41, 46, 55, 67, 70, 81, 86, 141.

Examples

			a(9) = A275316(10) - A275316(9) = 69120 - 66960 = 2160.
		

Crossrefs

Formula

a(n) = A275316(n+1) - A275316(n).

A275315 Average of amicable pairs (x,y), ordered by the smaller value x given in A002025.

Original entry on oeis.org

252, 1197, 2772, 5292, 6300, 10800, 13440, 17856, 69552, 66960, 69120, 78624, 84240, 112320, 131040, 122760, 147420, 155520, 174096, 178560, 194400, 199584, 322812, 349272, 374976, 378000, 446400, 477603, 508896, 524160, 635040, 648000, 657720, 673920, 648000, 725760, 761400, 833280, 890568, 939600
Offset: 1

Views

Author

Timothy L. Tiffin, Jul 22 2016

Keywords

Comments

Each term represents the midpoint of an interval (x,y), where x (A002025) and y (A002046) form a pair of amicable numbers (A259180). The length and radius of each interval can be found in A066539 and A162884, respectively.
This sequence is not monotonic (specifically, not nondecreasing), since x+y (A180164) is not monotonic. For a monotonic (nondecreasing) ordering of these averages, see A275316.
It is unknown if there exists an amicable pair where x and y have opposite parity (one is even and the other is odd). If such a pair is ever found, then the compound adjective "same-parity" will need to be added to the name of this sequence.

Examples

			a(  1) = (     220 +      284)/2 =      504/2 =      252.
a(  2) = (    1184 +     1210)/2 =     2394/2 =     1197.
a(  3) = (    2620 +     2924)/2 =     5544/2 =     2772.
...      ...                 ...          ...         ...
a(  9) = (   63020 +    76084)/2 =   139104/2 =    69552.
a( 10) = (   66928 +    66992)/2 =   133920/2 =    66960.
a( 11) = (   67095 +    71145)/2 =   138240/2 =    69120.
...      ...                 ...          ...         ...
a( 15) = (  122265 +   139815)/2 =   262080/2 =   131040.
a( 16) = (  122368 +   123152)/2 =   245520/2 =   122760.
a( 17) = (  141664 +   153176)/2 =   294840/2 =   147420.
...      ...                 ...          ...         ...
a( 32) = (  609928 +   686072)/2 =  1296000/2 =   648000.
...      ...                 ...          ...         ...
a( 35) = (  643336 +   652664)/2 =  1296000/2 =   648000.
...      ...                 ...          ...         ...
a(105) = ( 9478910 + 11049730)/2 = 20528640/2 = 10264320.
...      ...                 ...          ...         ...
a(109) = (10254970 + 10273670)/2 = 20528640/2 = 10264320.
...      ...                 ...          ...         ...
a(137) = (17754165 + 19985355)/2 = 37739520/2 = 18869760.
a(138) = (17844255 + 19895265)/2 = 37739520/2 = 18869760.
...      ...                 ...          ...         ...
		

Crossrefs

Formula

a(n) = [A002025(n) + A002046(n)]/2 = A180164(n)/2.

A275469 Difference between the larger and smaller terms of the n-th amicable pair (x,y) given in A259933.

Original entry on oeis.org

64, 26, 304, 544, 136, 112, 2310, 1120, 64, 4050, 13064, 18018, 8980, 23670, 784, 17550, 11512, 26420, 4480, 4576, 18064, 5720, 84544, 81304, 110852, 43184, 17888, 17150, 11680, 3510, 69296, 76144, 9328, 67072, 76592, 115592, 70592, 61110, 21712, 82768
Offset: 1

Views

Author

Timothy L. Tiffin, Jul 28 2016

Keywords

Comments

Each term represents the length of an interval (x,y), where x (A260086) and y (A260087) form a pair of amicable numbers (A259933). The midpoint and radius of each interval can be found in A275316 and A275470, respectively.
Each term will be even as long as there does not exist an amicable pair where x and y have opposite parity.
This sequence is a rearrangement of A066539 (which is based on A002025, A002046, and A259180). The first ten indices for which a(n) does not equal A066539(n) are n = 9, 10, 11, 15, 16, 33, 34, 35, 41, 42.

Examples

			a(1) = 284 - 220 = 64, a(2) = 1210 - 1184 = 26, and a(3) = 2924 - 2620 = 304.
		

Crossrefs

Formula

a(n) = A260087(n) - A260086(n).

A275470 Half the difference between the larger and smaller terms of the n-th amicable pair (x,y) given in A259933.

Original entry on oeis.org

32, 13, 152, 272, 68, 56, 1155, 560, 32, 2025, 6532, 9009, 4490, 11835, 392, 8775, 5756, 13210, 2240, 2288, 9032, 2860, 42272, 40652, 55426, 21592, 8944, 8575, 5840, 1755, 34648, 38072, 4664, 33536, 38296, 57796, 35296, 30555, 10856, 41384
Offset: 1

Views

Author

Timothy L. Tiffin, Jul 28 2016

Keywords

Comments

Each term represents the radius of an interval (x,y), where x (A260086) and y (A260087) form a pair of amicable numbers (A259933). The midpoint and length of each interval can be found in A275316 and A275469, respectively.
A term will be odd if and only if y-x = 2 mod 4. This occurs when x and y have the same parity but their average has the opposite parity.
This sequence is a rearrangement of A162884 (which is based on A002025, A002046, and A066539). The first ten indices for which a(n) does not equal A162884(n) are n = 9, 10, 11, 15, 16, 33, 34, 35, 41, 42.

Examples

			a(1) = (284-220)/2 = 64/2 = 32, a(2) = (1210-1184)/2 = 26/2 = 13, and a(3) = (2924-2620)/2 = 304/2 = 152.
		

Crossrefs

Formula

a(n) = [A260087(n) - A260086(n)]/2 = A275469(n)/2.
Showing 1-4 of 4 results.