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A076987 Smallest triangular number of the form n*k + 1 with k>0. +0
1
3, 3, 10, 21, 6, 55, 15, 105, 10, 21, 45, 253, 66, 15, 91, 465, 120, 55, 153, 21, 190, 45, 231, 1081, 276, 105, 28, 253, 378, 91, 435, 1953, 496, 171, 36, 253, 630, 153, 703, 561, 780, 253, 861, 45, 91, 231, 1035, 4465, 1128, 351, 1225, 105, 1326, 55, 276, 561 (list; graph; listen)
OFFSET

1,1

EXAMPLE

a(7) = 15 as 15 =7*2 + 1 is the smallest such triangular number.

MAPLE

a[1] := 3:for n from 2 to 175 do j := 2:while((j*(j+1)/2 mod n)<>1)do j := j+1:od: a[n] := j*(j+1)/2:od:seq(a[k], k=1..175);

CROSSREFS

Sequence in context: A077899 A049973 A025519 this_sequence A019153 A049975 A019168

Adjacent sequences: A076984 A076985 A076986 this_sequence A076988 A076989 A076990

KEYWORD

nonn

AUTHOR

Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Oct 25 2002

EXTENSIONS

Corrected and extended by Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de), Jan 26 2003

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Last modified September 5 19:23 EDT 2008. Contains 143485 sequences.


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