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A242739 Semiprimes having only straight digits. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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

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Last modified January 23 22:16 EST 2020. Contains 331177 sequences. (Running on oeis4.)