

A031980


a(n) = smallest number >= 1 not occurring earlier and not the sum of cubes of two distinct earlier terms.


6



1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 29, 30, 31, 32, 33, 34, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77
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OFFSET

1,2


REFERENCES

Mihaly Bencze [Beneze], Smarandache recurrence type sequences, Bulletin of pure and applied sciences, Vol. 16E, No. 2, 1997, pp. 231236.
F. Smarandache, Properties of numbers, ASU Special Collections, 1973.


LINKS

Klaus Brockhaus, Table of n, a(n) for n = 1..4900
F. Smarandache, Sequences of Numbers Involved in Unsolved Problems.
Eric Weisstein's World of Mathematics, Smarandache Sequences


MATHEMATICA

A031980 = {1}; Do[ m = Ceiling[(n1)^(1/3)]; s = Select[ A031980, # <= m &]; ls = Length[s]; sumOfCubes = Union[ Flatten[ Table[ s[[i]]^3 + s[[j]]^3, {i, 1, ls}, {j, i+1, ls}]]]; If[ FreeQ[ sumOfCubes, n], AppendTo[ A031980, n] ], {n, 2, 77}]; A031980 (* JeanFrançois Alcover, Dec 14 2011 *)


PROG

(MAGMA) m:=77; a:=[]; a2:={}; for n in [1..m] do p:=1; u:= a2 join { x: x in a }; while p in u do p:=p+1; end while; if p gt m then break; end if; a2:=a2 join { x^3 + p^3: x in a  x^3 + p^3 le m }; Append(~a, p); end for; print a; /* Klaus Brockhaus, Jul 16 2008 */


CROSSREFS

Cf. A024670 (sums of cubes of two distinct positive integers), A001235 (sums of two cubes in more than one way), A141805 (complement).
Sequence in context: A265556 A004728 A072886 * A183221 A317492 A324721
Adjacent sequences: A031977 A031978 A031979 * A031981 A031982 A031983


KEYWORD

nonn,nice,easy


AUTHOR

J. Castillo (arp(AT)ciag.com) [Broken email address?]


EXTENSIONS

More terms from Larry Reeves (larryr(AT)acm.org), Sep 26 2000
Better definition from Klaus Brockhaus, Jul 16 2008


STATUS

approved



