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Search: id:A089988
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| A089988 |
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Possible differences of n^2*(n+1)/2. |
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+0
1
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| 5, 12, 17, 22, 34, 35, 39, 51, 57, 69, 70, 74, 86, 92, 108, 117, 120, 121, 125, 145, 156, 162, 176, 178, 190, 195, 209, 210, 213, 247, 248, 262, 270, 279, 282, 287, 321, 330, 354, 365, 376, 386, 387, 399, 404, 424
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Vaguely related to x^3+y^3=z^3, as x^3=2x.A000217(x) - x^2, e.g. 3^3=2.3.6 - 9 = 27.
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FORMULA
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n^2*(n+1)/2 - m^2*(m+1)/2 for all n>m
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EXAMPLE
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5^2*(5+1)/2=25*3=75 and 3^2*(3+1)/2=9*2=18, so 75-18=57 is in the sequence
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PROGRAM
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(PARI) { v=vector(300); c=0; for (i=1, 20, for (j=i, 20, v[c++ ]=tn(j)-tn(i))); v=vecsort(v); v }
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CROSSREFS
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Cf. A000217, A002411 (pentagonal pyramidal numbers).
Sequence in context: A008467 A076718 A076671 this_sequence A135459 A063297 A022137
Adjacent sequences: A089985 A089986 A089987 this_sequence A089989 A089990 A089991
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KEYWORD
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nonn
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AUTHOR
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Jon Perry (perry(AT)globalnet.co.uk), Jan 14 2004
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