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 A280576 Primes formed from the concatenation of previousprime(n) and n. 1
 23, 79, 3137, 3739, 4751, 6163, 8387, 8389, 109111, 113117, 113123, 151153, 151157, 157163, 167173, 173177, 181183, 199207, 199211, 211213, 211217, 211219, 233239, 241249, 251257, 257263, 263267, 263269, 271273, 271277, 277279, 283289, 317321, 317323, 317327 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS K. D. Bajpai, Table of n, a(n) for n = 1..7768 EXAMPLE 79 is in the sequence because it is a prime formed from the concatenation of 7 and 9, where 7 is the largest prime < 9. 8387 is in the sequence because it is a prime formed from the concatenation of 83 and 87, where 83 is the largest prime < 87. MATHEMATICA Select[Table[FromDigits[Join[IntegerDigits[Prime[PrimePi[n - 1]]], IntegerDigits[n]]], {n, 3, 1000}], PrimeQ] PROG (Magma) [p : n in[3..200] | IsPrime (p) where p is Seqint (Intseq (n) cat Intseq (PreviousPrime (n)))]; (PARI) terms(n) = my(i=0, x=3); while(1, my(cc=eval(Str(precprime(x-1), x))); if(ispseudoprime(cc), print1(cc, ", "); i++); if(i==n, break); x++) /* Print initial 40 terms as follows: */ terms(40) \\ Felix FrÃ¶hlich, Jan 05 2017 CROSSREFS Cf. A000040, A084667, A084669, A151799, A151800, A280357, A280388. Sequence in context: A141974 A142650 A078597 * A160297 A210706 A304592 Adjacent sequences:  A280573 A280574 A280575 * A280577 A280578 A280579 KEYWORD nonn,base AUTHOR K. D. Bajpai, Jan 05 2017 STATUS approved

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Last modified August 11 00:32 EDT 2020. Contains 336403 sequences. (Running on oeis4.)