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A161706 (-11*n^5 + 145*n^4 - 635*n^3 + 1115*n^2 - 494*n + 120)/120. 20
1, 2, 4, 5, 10, 20, 21, -27, -201, -626, -1486, -3035, -5608, -9632, -15637, -24267, -36291, -52614, -74288, -102523, -138698, -184372, -241295, -311419, -396909, -500154, -623778, -770651, -943900, -1146920, -1383385, -1657259, -1972807 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

{a(k): 0 <= k < 6} = divisors of 20:

a(n) = A027750(A006218(19) + k + 1), 0 <= k < A000005(20).

LINKS

Table of n, a(n) for n=0..32.

R. Zumkeller, Enumerations of Divisors

Index entries for linear recurrences with constant coefficients, signature (6,-15,20,-15,6,-1).

FORMULA

a(n) = C(n,0) + C(n,1) + C(n,2) - 2*C(n,3) + 7*C(n,4) - 11*C(n,5).

G.f.: (1-4*x+7*x^2-9*x^3+15*x^4-21*x^5)/(1-x)^6. - Colin Barker, Apr 25 2012

EXAMPLE

Differences of divisors of 20 to compute the coefficients of their interpolating polynomial, see formula:

1 ... 2 ... 4 ... 5 ... 10 ... 20

.. 1 ... 2 ... 1 ... 5 ... 10

..... 1 .. -1 ... 4 ... 5

....... -2 ... 5 ... 1

........... 7 .. -4

............ -11.

PROG

(MAGMA)[(-11*n^5 + 145*n^4 - 635*n^3 + 1115*n^2 - 494*n + 120)/120: n in [0..50]]; [From Vincenzo Librandi, Dec 27 2010]

(PARI) a(n)=(-11*n^5+145*n^4-635*n^3+1115*n^2-494*n+120)/120 \\ Charles R Greathouse IV, Sep 24 2015

CROSSREFS

A005408, A000124, A016813, A086514, A000125, A058331, A002522, A161701, A161702, A161703, A000127, A161704, A161707, A161708, A161710, A080856, A161711, A161712, A161713, A161715, A006261.

A005018, A161700, A161856. - Reinhard Zumkeller, Jun 21 2009

Sequence in context: A005018 A249399 A118551 * A128401 A018467 A035524

Adjacent sequences:  A161703 A161704 A161705 * A161707 A161708 A161709

KEYWORD

sign,easy

AUTHOR

Reinhard Zumkeller, Jun 17 2009

STATUS

approved

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Last modified May 30 06:51 EDT 2017. Contains 287302 sequences.