The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A158864 Prepending 6 to n-th triangular number produces a prime. 1
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Or, concatenated T(3) and T(n) are prime. Or, concatenated A000217(3) and A000217(n) are prime. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 EXAMPLE n=13: T(13)=91, 691 is prime, n=37: T(37)=703, 6703 is prime, n=73: T(73)=2701, 62701 is prime. MATHEMATICA Rest[Flatten[Position[Accumulate[Range[3000]], _?(PrimeQ[ 6*10^IntegerLength[ #]+#]&)]]] (* Harvey P. Dale, Jul 27 2015 *) CROSSREFS A158844 Concatenated triangular numbers T(n), T(n + 1) and T(n + 2) are prime. A158862 Prepending 3 to n-th triangular number produces a prime. A158845 Prepending 1 to n-th triangular number produces a prime. A158750 Concatenated triangular numbers that are prime. A000217 Triangular numbers. Sequence in context: A049742 A247867 A113601 * A003154 A083577 A155285 Adjacent sequences:  A158861 A158862 A158863 * A158865 A158866 A158867 KEYWORD base,nonn AUTHOR Zak Seidov, Mar 28 2009 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified June 15 11:10 EDT 2021. Contains 345048 sequences. (Running on oeis4.)