A087385 a(n) = smallest prime == 1 (mod T(n)) where T(n) is the n-th triangular number (A000217).

2, 7, 7, 11, 31, 43, 29, 37, 181, 331, 67, 79, 547, 211, 241, 137, 307, 2053, 191, 211, 463, 1013, 277, 601, 1301, 3511, 379, 2437, 1741, 1861, 1489, 2113, 1123, 2381, 631, 1999, 4219, 1483, 2341, 821, 1723, 3613, 947, 991, 6211, 12973, 1129, 3529, 7351

Offset

1,1

Links

Table of n, a(n) for n=1..49.

Example

The prime corresponding to the triangular number 21 is 43.

Mathematica

sm1[n_]:=Module[{p=NextPrime[n]}, While[Mod[p, n]!=1, p=NextPrime[p]]; p]; Join[ {2}, Table[sm1[(n(n+1))/2], {n, 2, 50}]] (* Harvey P. Dale, May 29 2020 *)

Crossrefs

Sequence in context: A316352 A114532 A003061 * A168278 A267499 A351583

Adjacent sequences: A087382 A087383 A087384 * A087386 A087387 A087388

Keyword

nonn

Author

Amarnath Murthy, Sep 09 2003

Extensions

More terms from Sam Alexander, Dec 28 2003

Status

approved