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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

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