A076987 Smallest triangular number of the form n*k + 1 with k>0.

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

Offset

1,1

Links

Table of n, a(n) for n=1..56.

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: A049973 A025519 A360651 * A229912 A321354 A019153

Adjacent sequences: A076984 A076985 A076986 * A076988 A076989 A076990

Keyword

nonn

Author

Amarnath Murthy, Oct 25 2002

Extensions

Corrected and extended by Sascha Kurz, Jan 26 2003

Status

approved