The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A155025 Primes p=A000040(n) with nonprime index n such that the concatenation n//p is a composite number. 2
 2, 19, 23, 29, 43, 47, 53, 71, 73, 79, 89, 97, 101, 107, 131, 137, 139, 163, 167, 173, 193, 223, 227, 229, 233, 239, 257, 281, 293, 307, 311, 313, 317, 337, 347, 349, 359, 373, 379, 383, 389, 397, 409, 419, 433, 443, 449, 457, 463, 467, 491, 499, 503, 521, 541, 557, 569 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..10000 EXAMPLE For the nonprime n=1, p = prime(n) = 2, the concatenation is 12 is composite, and p is added to the sequence. For the nonprime n=8, p = prime(8) = 19, the concatenation 819 is composite, and p=19 is added to the sequence. For the nonprime n=12, p = prime(12) = 37, the concatenation 1237 is prime, so p=37 is not added to the sequence. MATHEMATICA cnQ[{n_, p_}]:=!PrimeQ[n]&&!PrimeQ[FromDigits[Flatten[ IntegerDigits/@ {n, p}]]]; Transpose[Select[Table[{n, Prime[n]}, {n, 150}], cnQ]][[2]] (* Harvey P. Dale, Dec 18 2012 *) CROSSREFS Cf. A000040, A003808, A141468, A155030. Sequence in context: A268492 A130112 A019348 * A191068 A069690 A037003 Adjacent sequences: A155022 A155023 A155024 * A155026 A155027 A155028 KEYWORD nonn,base AUTHOR Juri-Stepan Gerasimov, Jan 19 2009 EXTENSIONS Definition clarified, sequence extended by R. J. Mathar, Oct 14 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 9 04:13 EST 2022. Contains 358698 sequences. (Running on oeis4.)