A117159 Prime numbers for which the multiplicative digital root is also a prime number.

2, 3, 5, 7, 13, 17, 31, 37, 43, 53, 71, 73, 113, 131, 137, 151, 157, 173, 211, 223, 311, 317, 359, 367, 389, 431, 557, 571, 593, 673, 751, 827, 839, 929, 953, 983, 1117, 1151, 1153, 1171, 1223, 1279, 1297, 1367, 1447, 1511, 1531, 1553, 1571, 1579, 1597, 1621

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

157 is in the sequence because it is a prime number and its multiplicative digital root 5 is also a prime number.

Mathematica

a[n_]:=NestWhile[Times@@IntegerDigits[#]&, n, #>9&]; Select[Prime[Range[258]], PrimeQ[a[#]]&] (* Jayanta Basu, Jun 02 2013 *)

Crossrefs

Intersection of A000040 and A028843.

Cf. A031347.

Sequence in context: A048975 A009571 A087520 * A134873 A172979 A118724

Adjacent sequences: A117156 A117157 A117158 * A117160 A117161 A117162

Keyword

base,nonn

Author

Luc Stevens (lms022(AT)yahoo.com), Apr 21 2006; corrected Apr 30 2006

Status

approved