

A154508


Numbers k such that appending k to the kth nonprime yields a prime.


0



3, 7, 9, 19, 23, 41, 43, 53, 57, 59, 63, 67, 97, 141, 147, 177, 221, 237, 239, 251, 281, 289, 291, 299, 313, 333, 339, 343, 363, 367, 373, 379, 383, 449, 457, 459, 463, 467, 489, 497, 503, 507, 527, 529, 539, 547, 563, 569, 579, 583, 597, 599, 601, 603, 607
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OFFSET

1,1


COMMENTS

Previous title: "Numbers n if concatenation of nth nonprime and n = prime."
Indices n such that the concatenation A141468(n)//n yields a prime.  R. J. Mathar, Jan 12 2009


LINKS



EXAMPLE

Since 4=nonprime(3) and 43 is prime, 3 is in this sequence.
Since 10=nonprime(7) and 107 is prime, 7 is in this sequence.
Since 14=nonprime(9) and 149 is prime, 9 is in this sequence.
Since 27=nonprime(23) and 3323 is prime, 23 is in this sequence.
Since 56=nonprime(41) and 5641 is prime, 41 is in this sequence, etc.
The sequence A141468 concatenated with the positive nonzero integers begins 1, 12, 43, 64, 85, 96, 107, 128, 149, 1510, 1611, ... Among these terms, 43, 107, and 149 are primes, so 3, 7, and 9 are in this sequence.  Charlie Neder, Dec 23 2018


MAPLE

A141468 := proc(n) option remember ; local a; if n <=2 then n1 ; else for a from procname(n1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end: cat2 := proc(a, b) local d; d := max(1, ilog10(b)+1) ; a*10^d+b ; end: for n from 1 to 1000 do p := cat2( A141468(n), n) ; if isprime(p) then printf("%d, ", n ) ; fi; od: # R. J. Mathar, Jan 12 2009


CROSSREFS



KEYWORD

nonn,base,less


AUTHOR



EXTENSIONS



STATUS

approved



