A069832 Prefixing, suffixing or inserting a 7 in the number anywhere gives a prime.

1, 3, 9, 19, 27, 33, 39, 57, 87, 97, 159, 177, 187, 433, 487, 541, 603, 691, 717, 753, 757, 853, 949, 1257, 1471, 1707, 2277, 2367, 2617, 2953, 4317, 4507, 4623, 4779, 4797, 5773, 6481, 6757, 6777, 7017, 7351, 7417, 7471, 7479, 7747, 7797, 7813, 7977

Offset: 1

Author

Amarnath Murthy, Apr 14 2002

Keywords

• base
• nonn

Links

• Giovanni Resta, Table of n, a(n) for n = 1..2399 (terms < 10^13, first 201 terms from Harvey P. Dale)

Crossrefs

Cf. A068674, A068679, A069833.

Programs

Mathematica

psi7Q[n_]:=Module[{idn=IntegerDigits[n]},And@@PrimeQ[FromDigits/@ Table[ Insert[ idn,7,i],{i,Length[idn]+1}]]]; Select[Range[8000],psi7Q] (* Harvey P. Dale, Sep 18 2012 *)

Extensions

More terms from Vladeta Jovovic, Apr 16 2002

Offset changed to 1 by Giovanni Resta, Oct 14 2019