A242989 Numbers n such that concatenating 1 with four instances of n produces a prime.

37, 39, 49, 73, 97, 123, 139, 159, 211, 213, 219, 253, 273, 291, 313, 327, 337, 339, 369, 399, 409, 477, 481, 511, 529, 531, 579, 589, 607, 633, 643, 663, 697, 717, 723, 733, 753, 787, 789, 819, 831, 841, 891, 909, 919, 967, 987, 1041, 1117, 1131, 1281, 1377

Offset

1,1

Links

Jens Kruse Andersen, Table of n, a(n) for n = 1..10000

Example

159 is included because 1159159159159 is a prime.

Mathematica

cQ[n_, i_]:=Module[{idn=IntegerDigits[n]}, PrimeQ[FromDigits[Flatten[ Join[ {1}, Table[ idn, {i}]]]]]]; Select[Range[2000], cQ[#, 4]&]

Prog

(Python)
from sympy import isprime
for n in range(10**3):
..if isprime('1'+4*str(n)):
....print(n, end=', ')
# Derek Orr, Aug 17 2014
(PARI) s=[]; for(n=1, 10^4, d=length(Str(n)); if(isprime(10^(4*d)+(10^(4*d)-1)/(10^d-1)*n), s=concat(s, n))); s \\ Jens Kruse Andersen, Aug 18 2014

Crossrefs

Cf. A242987, A242988, A242990.

Sequence in context: A111043 A041683 A064172 * A345481 A295801 A111198

Adjacent sequences: A242986 A242987 A242988 * A242990 A242991 A242992

Keyword

nonn,base,easy

Author

Harvey P. Dale, Aug 17 2014

Status

approved