A158864 Numbers k such that prepending 6 to the k-th triangular number produces a prime.

13, 37, 73, 118, 166, 217, 313, 433, 457, 493, 538, 541, 553, 601, 613, 637, 706, 826, 853, 898, 958, 1042, 1057, 1138, 1222, 1357, 1441, 1513, 1666, 1681, 1777, 1858, 1966, 1993, 2173, 2281, 2341, 2422, 2446, 2518, 2626, 2638, 2653, 2686, 2701, 2737

Offset

1,1

Comments

Or, concatenated T(3) and T(k) are prime. Or, concatenated A000217(3) and A000217(k) are prime.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

T(13)=91, 691 is prime, so 13 is a term;
T(37)=703, 6703 is prime, so 37 is a term;
T(73)=2701, 62701 is prime, so 73 is a term.

Mathematica

Rest[Flatten[Position[Accumulate[Range[3000]], _?(PrimeQ[ 6*10^IntegerLength[ #]+#]&)]]] (* Harvey P. Dale, Jul 27 2015 *)

Crossrefs

Cf. A000217, A158844, A158862, A158845, A158750.

Sequence in context: A347209 A247867 A113601 * A003154 A083577 A155285

Adjacent sequences: A158861 A158862 A158863 * A158865 A158866 A158867

Keyword

base,nonn

Author

Zak Seidov, Mar 28 2009

Status

approved