A185973 - OEIS

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A185973

Array of divisor product arguments appearing in the denominator of the unique representation of primorials A002110 in terms of divisor products.

1, 3, 2, 15, 10, 6, 1, 105, 70, 42, 30, 7, 5, 3, 2, 1155, 770, 462, 330, 210, 77, 55, 35, 33, 22, 21, 15, 14, 10, 6, 1, 15015, 10010, 6006, 4290, 2730, 2310, 1001, 715, 455, 429, 385, 286, 273, 231, 195, 182, 165, 154, 130, 110, 105, 78, 70, 66, 42, 30, 13, 11, 7, 5, 3, 2, 255255, 170170, 102102, 72930, 46410, 39270, 30030, 17017, 12155, 7735, 7293, 6545, 5005, 4862, 4641, 3927, 3315, 3094, 3003, 2805, 2618, 2210, 2145, 2002, 1870, 1785, 1430, 1365, 1326, 1190, 1155, 1122, 910, 858, 770, 714, 546, 510, 462, 390, 330, 221, 210, 187, 143, 119, 91, 85, 77, 65, 55, 51, 39, 35, 34, 33, 26, 22, 21, 15, 14, 10, 6, 1

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OFFSET

1,2

COMMENTS

The corresponding array for the numerators is given as A185972(n,m).

The sequence of row lengths of this array is 2^{n-1}=A000079(n-1), n>=1.

The array a(n,m), m=1..2^{n-1}, n>=1, is to be read as an ordered list of numbers which give the arguments for the divisor products, called dp(). E.g., in row n=2: [3,2] stands for the ordered product

dp(3) dp(2). Only after evaluation dp(k) becomes A007955(k).

Every natural number has a unique representation in terms of divisor products dp( ) which become after evaluation A007955(k). This representation is called dpr(n). The one for the primorials n=A002110(N), N>=1, is fundamental.

See the W. Lang link given in A185972, and also under A007955.

LINKS

Table of n, a(n) for n=1..127.

W. Lang: First 8 rows, also for A185972.

FORMULA

a(n,m), together with A185972(n,m), is found using proposition 1 of a paper by W. Lang, given as link in A185972. In this proposition p_j has, for the application here, to be replaced by the j-th prime p(j):=A000040(j), and a() there is dp() here.

EXAMPLE

[1],[3,2],[15,10,6,1],[105,70,42,30,7,5,3,2],...

The numerator/denominator structure begins

[2]/[1]; [6, 1]/[3, 2]; [30, 5, 3, 2]/[15, 10, 6, 1], [210, 35, 21, 15, 14, 10, 6, 1]/[105, 70, 42, 30, 7, 5, 3, 2],...

n=3: A002110(3)=30 has the unique representation symbolized by [30, 5, 3, 2]/[15, 10, 6, 1] which is

dp(30) dp(5) dp(3) dp(2)/dp(15) dp(10) dp(6) dp(1). Note that dp(1),although it evaluates to 1 has to be kept in the representation. This checks: (30*15*10*6*5*3*2*1)*(5*1)*(3*1)*(2*1)/

((15*5*3*1)*(10*5*2*1)*(6*3*2*1)*(1)) = 30.

CROSSREFS

Cf.: A007955.

Sequence in context: A199167 A218969 A345291 * A258566 A374667 A051917

Adjacent sequences: A185970 A185971 A185972 * A185974 A185975 A185976

KEYWORD

nonn,easy,tabf

AUTHOR

Wolfdieter Lang, Feb 08 2011

STATUS

approved