A110705 Numbers k such that "k 42's followed by 43" is prime.

0, 1, 2, 3, 4, 7, 17, 24, 59, 199, 743, 2558, 4896, 5539, 6192, 10977, 27679, 42158

Offset

1,3

Comments

Equivalently, a(n) generates primes of the form (100^(1+a(n)) - 1) * 42/99 + 1. - Mohsen Hozan, Jan 23 2015

Links

Table of n, a(n) for n=1..18.

Carlo Corti, A110705: segmented PFGW search for OEIS sequence A110705 through n=45000.

Mathematica

t = 1; Do[ t = t*100 - 57; If[PrimeQ[t], Print[n]], {n, 0, 200}]
(* Alternative: *)
robinsonQ[n_] := PrimeQ[(100^(1 + n) - 1) * 42/99 + 1]; Select[Range[0, 200], robinsonQ] (* Robert G. Wilson v, Jan 23 2015 *)

Prog

(PARI) t=1; for(n=0, 10^6, t=100*t-57; if(ispseudoprime(t), print1(n, ", "))); \\ Joerg Arndt, Nov 21 2014
(PFGW) ABC2 1+(100^(1+$a)-1)*42/99
a: from 0 to 28000 \\ Charles R Greathouse IV, Mohsen Hozan, Jan 23 2015

Crossrefs

Cf. A110704, A254002.

Sequence in context: A375283 A179985 A338928 * A139439 A376735 A352902

Adjacent sequences: A110702 A110703 A110704 * A110706 A110707 A110708

Keyword

nonn,base,hard,more,changed

Author

Ray Chandler, Aug 04 2005

Extensions

a(13)-a(17) from Mohsen Hozan, Feb 10 2015

a(18) from Carlo Corti, Jun 25 2026

Status

approved