

A004210


"Magic" integers: a(n+1) is the smallest integer m such that there is no overlap between the sets {m, ma(i), m+a(i): 1 <= i <= n} and {a(i), a(i)a(j), a(i)+a(j): 1 <= j < i <= n}.
(Formerly M2728)


5



1, 3, 8, 18, 30, 43, 67, 90, 122, 161, 202, 260, 305, 388, 416, 450, 555, 624, 730, 750, 983, 1059, 1159, 1330, 1528, 1645, 1774, 1921, 2140, 2289, 2580, 2632, 2881, 3158, 3304, 3510, 3745, 4086, 4563, 4741, 4928, 5052, 5407, 5864, 6242, 6528, 6739, 7253
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OFFSET

1,2


COMMENTS

The definition implies that the sets {a(i)} (A004210), {a(i)a(j), j < i} (A206522) and {a(i)+a(j), j < i} (A206523) are disjoint. A206524 gives the complement of their union.


REFERENCES

D. R. Hofstadter, "Goedel, Escher, Bach: An Eternal Golden Braid", Basic Books Incorporated, p. 73
P. Mark Kayll, Wellspread sequences and edgelabelings with constant Hamiltonian weight, Disc. Math. & Theor. Comp. Sci 6 2 (2004) 401408
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

T. D. Noe, Table of n, a(n) for n = 1..150
B. G. DeBoer, Letter to N. J. A. Sloane, Dec 15 1978, with enclosure of Silvertom article.
J. V. Silverton, On the generation of 'magic integrals', Acta Cryst. A34 (1978) p. 634.
Eric Weisstein's World of Mathematics, Magic Integer.


FORMULA

a(n+1) = min{ k  k and k + a(i) are not equal to a(i) or a(i)a(j) or a(i)+a(j) for any n+1 > i > j > 0}. [Corrected by T. D. Noe, Sep 08 2008]


MATHEMATICA

a[1] = 1; a[n_] := a[n] = Module[{pairs = Flatten[ Table[{a[j] + a[k], a[k]  a[j]}, {j, 1, n1}, {k, j+1, n1}]], an = a[n1] + 1}, While[ True, If[ Intersection[ Join[ Array[a, n1], pairs], Prepend[ Flatten[ Table[{a[j] + an, an  a[j]}, {j, 1, n1}]], an]] == {}, Break[], an++]]; an]; Table[a[n], {n, 1, 48}] (* JeanFrançois Alcover, Nov 10 2011 *)


PROG

(Haskell)
import Data.List (intersect)
a004210 n = a004210_list !! (n1)
a004210_list = magics 1 [0] [0] where
magics :: Integer > [Integer] > [Integer] > [Integer]
magics n ms tests
 tests `intersect` nMinus == [] && tests `intersect` nPlus == []
= n : magics (n+1) (n:ms) (nMinus ++ nPlus ++ tests)
 otherwise
= magics (n+1) ms tests
where nMinus = map (n ) ms
nPlus = map (n +) ms
 magics works also as generator for a126428_list, cf. A126428.
 Reinhard Zumkeller, Mar 03 2011


CROSSREFS

Cf. A000969, A005228, A206522, A206523, A206524.
Sequence in context: A063597 A171701 A288249 * A247022 A119881 A184636
Adjacent sequences: A004207 A004208 A004209 * A004211 A004212 A004213


KEYWORD

easy,nonn,nice


AUTHOR

N. J. A. Sloane, following a suggestion from B. G. DeBoer, Dec 15 1978


EXTENSIONS

Additional comments from Robert M. Burton, Jr. (bob(AT)oregonstate.edu), Feb 20 2005
More terms from Joshua Zucker, May 04 2006
Edited by N. J. A. Sloane, Sep 06 2008 at the suggestion of R. J. Mathar
Edited by N. J. A. Sloane, Feb 08 2012


STATUS

approved



