login
A112394
Smallest prime obtained by appending 3's to k, where k runs through the numbers not divisible by 3, or -1 if no such prime exists.
3
13, 23, 43, 53, 73, 83, 103, 113, 1333333333333333, 1433, 163, 173, 193, 20333, 223, 233, 2533333333, 263, 283, 293, 313, 323333, 3433, 353, 373, 383
OFFSET
1,1
COMMENTS
Next term is 40 followed by 483 3's, and is too large to display here (see the b-file).
LINKS
Toshitaka Suzuki, Table of n, a(n) for n = 1..273 (terms 1..200 from Harvey P. Dale)
EXAMPLE
For k = 1, we get the prime 13.
For k = 13, we get the prime 1333333333333333 (the smaller numbers 133,1333,13333 etc. are not primes).
For k = 4070 and 9287, no such prime exists, so we get -1 for the value. Compare A372056. - Toshitaka Suzuki, Mar 30 2024
MATHEMATICA
sp3[n_]:=Module[{idn=IntegerDigits[n], k=1}, While[!PrimeQ[FromDigits[ Join[ idn, PadRight[ {}, k, 3]]]], k++]; FromDigits[Join[idn, PadRight[{}, k, 3]]]]; sp3/@Drop[Range[40], {3, -1, 3}] (* Harvey P. Dale, Jul 11 2017 *)
CROSSREFS
See A372056 for another version.
Sequence in context: A119488 A165350 A236418 * A067227 A240113 A256177
KEYWORD
nonn,base
AUTHOR
Parthasarathy Nambi, Dec 05 2005
EXTENSIONS
More terms from Lambert Herrgesell (zero815(AT)googlemail.com), Dec 09 2005
Edited by N. J. A. Sloane, Apr 24 2024. (Escape clause added to definition at the suggestion of Toshitaka Suzuki, Mar 30 2024. See also A372056.)
STATUS
approved