A242739 Semiprimes having only straight digits.

4, 14, 74, 77, 111, 141, 177, 411, 417, 447, 471, 717, 771, 1111, 1114, 1141, 1147, 1174, 1177, 1411, 1417, 1441, 1477, 1711, 1714, 1717, 1774, 4117, 4141, 4171, 4174, 4411, 4414, 4417, 4471, 4474, 4711, 4714, 4717, 4741, 4747, 4771, 4777, 7111, 7114, 7117, 7141

Offset

1,1

Comments

A straight digit semiprime has only the straight digits, i.e., 1, 4 or 7.

Intersection of A001358 and A028373. - Michel Marcus, May 25 2014

Links

K. D. Bajpai, Table of n, a(n) for n = 1..1727

Example

471 = 3 * 157 is semiprime and has only straight digits 4, 7 and 1. Hence it is in the sequence.
1147 =  31 * 37 is semiprime and has only straight digits 1, 1, 4 and 7. Hence it is in the sequence.

Mathematica

A242739 = {}; Do[a = PrimeOmega[n]; If [a == 2 && Intersection[IntegerDigits[n], {0, 2, 3, 5, 6, 8, 9}] == {}, AppendTo[A242739, n]], {n, 8000}]; A242739
Table[Select[FromDigits/@Tuples[{1, 4, 7}, n], PrimeOmega[#]==2&], {n, 4}]//Flatten (* Harvey P. Dale, Sep 23 2022 *)

Crossrefs

Cf. A001358, A028373, A079651, A108631, A108632.

Sequence in context: A167144 A159483 A088127 * A007282 A222900 A222485

Adjacent sequences: A242736 A242737 A242738 * A242740 A242741 A242742

Keyword

nonn,base

Author

K. D. Bajpai, May 21 2014

Status

approved