

A138591


Sums of two or more consecutive nonnegative integers.


15



1, 3, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 33, 34, 35, 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, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77
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OFFSET

1,2


COMMENTS

Closely related to but different from A057716.  N. J. A. Sloane, May 16 2008
These are called polite numbers [From Howard Berman (howard_berman(AT)hotmail.com), Oct 29 2008] by those who require nonnegative integers in the definition as opposed to positive integers. With the latter requirement, 1 = 0 + 1 does not count as a polite number. [This difference of definition pointed out by Ant King (Nov 19 2010)] There is no disagreement that 1 belongs in this sequence, but there is disagreement as to whether it counts as a polite number.
Of course sums of two or more consecutive nonpositive integers have the same absolute values (noted while inserting "nonnegative" in title). All integers are sums of two or more consecutive integers without such restriction.  Rick L. Shepherd, Jun 03 2014
In K12 education, these are known as "staircase numbers." The "1" is often omitted.  Gordon Hamilton, Mar 17 2015


REFERENCES

A. Wah and H. Picciotto, Algebra: Themes, Tools, Concepts, 1994, page 190.


LINKS

Table of n, a(n) for n=1..71.
Erzsébet Orosz, On oddsumming numbers, Acia Academiae Paedagogicae Agriensis, Seciio Maihemaiicae 31 (2004), pp. 125129.
Ron Knott, An Introduction to Runsums
Mathedpage, Staircases
NRICH, Polite numbers
Melfried Olson, Sequentially so, Mathematics Magazine 52:5, pp. 297298.
PlanetMath, Polite number
Wai Yan Pong, Sums of consecutive integers, The College Mathematics Journal, 38 (2007), 119123.  Parthasarathy Nambi, May 20 2009
Wikipedia, Polite number


FORMULA

a(n) = n + A000523(n + A000523(n)).  Charles R Greathouse IV, Aug 12 2010


EXAMPLE

0+1=1, 1+2=3, 2+3=5, 1+2+3=6, 3+4=7, 4+5=9, 1+2+3+4=10, ...


MATHEMATICA

Array[r, 9]; k = 0; For[i = 0, i <= 33, a = i; For[j = i + 1, j <= 34, a = a + j; k++; r[k] = a; j++]; i++]; q = Union[Array[r, k]]; StringTake[ToString[q], 99]
1 + # + Floor[Log[2, # + 1 + Log[2, # + 1]]] &/@Range[0, 70] (* Ant King, Nov 18 2010 *)


CROSSREFS

Cf. A057716.
Sequence in context: A079581 A229858 A057716 * A136492 A062506 A213199
Adjacent sequences: A138588 A138589 A138590 * A138592 A138593 A138594


KEYWORD

nonn,easy,changed


AUTHOR

Vladimir Joseph Stephan Orlovsky, May 13 2008


EXTENSIONS

More terms from Carl R. White, Jul 22 2009
Comment regarding polite numbers edited by Ant King, Nov 19 2010


STATUS

approved



