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A188377 a(n) = n^3 - 4n^2 + 6n - 2. 20
7, 22, 53, 106, 187, 302, 457, 658, 911, 1222, 1597, 2042, 2563, 3166, 3857, 4642, 5527, 6518, 7621, 8842, 10187, 11662, 13273, 15026, 16927, 18982, 21197, 23578, 26131, 28862, 31777, 34882, 38183, 41686, 45397, 49322, 53467, 57838, 62441, 67282, 72367 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

Number of nilpotent elements in the identity difference partial one - one transformation semigroup, denoted by N(IDI_n).

a(n+1) is also the Moore lower bound on the order of an (n,7)-cage. - Jason Kimberley, Oct 20 2011

REFERENCES

A. Laradji and A. Umar, On the number of nilpotents in the partial symmetric semigroup, Communications in Algebra 32 (2004), 3017-3023.

R. P. Sullivan, Semigroups generated by nilpotent transformations, Journal of Algebra 110 (1987), 324-345.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 3..1000

G. Royle, Cages of higher valency

Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).

FORMULA

a(n+1) = (n+1)^3 - 4*(n+1)^2 + 6*(n+1) - 2

       = (n-1)^3 + 2*(n-1)^2 + 2*(n-1) + 2

       = 1222 read in base n-1.

- Jason Kimberley, Oct 20 2011

From Colin Barker, Apr 06 2012: (Start)

a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4).

G.f.: x^3*(7 - 6*x + 7*x^2 - 2*x^3)/(1-x)^4. (End)

EXAMPLE

For n=3, #N(IDI_n) = 7.

MATHEMATICA

Table[n^3 - 4*n^2 + 6*n - 2, {n, 3, 80}] (* Vladimir Joseph Stephan Orlovsky, Jul 07 2011 *)

PROG

(MAGMA) [n^3 - 4*n^2 + 6*n - 2: n in [3..50]]; // Vincenzo Librandi, May 01 2011

(MAGMA) [SequenceToInteger([2^^3, 1], n-2):n in [5..50]]; // Jason Kimberley, Oct 20 2011

(PARI) a(n)=n^3-4*n^2+6*n-2 \\ Charles R Greathouse IV, Apr 06 2012

CROSSREFS

Cf. A188716, A188947.

Moore lower bound on the order of a (k,g) cage: A198300 (square); rows: A000027 (k=2), A027383 (k=3), A062318 (k=4), A061547 (k=5), A198306 (k=6), A198307 (k=7), A198308 (k=8), A198309 (k=9), A198310 (k=10), A094626 (k=11); columns: A020725 (g=3), A005843 (g=4), A002522 (g=5), A051890 (g=6), this sequence (g=7). - Jason Kimberley, Oct 30 2011

Sequence in context: A011926 A101120 A151717 * A213585 A246831 A122238

Adjacent sequences:  A188374 A188375 A188376 * A188378 A188379 A188380

KEYWORD

nonn,easy

AUTHOR

Adeniji, Adenike & Makanjuola, Samuel (somakanjuola(AT)unilorin.edu.ng) Apr 14 2011

EXTENSIONS

Edited by N. J. A. Sloane, Apr 23 2011

STATUS

approved

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Last modified February 25 20:40 EST 2018. Contains 299656 sequences. (Running on oeis4.)