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A276039 Numbers using only digits 1 and 7. 9
1, 7, 11, 17, 71, 77, 111, 117, 171, 177, 711, 717, 771, 777, 1111, 1117, 1171, 1177, 1711, 1717, 1771, 1777, 7111, 7117, 7171, 7177, 7711, 7717, 7771, 7777, 11111, 11117, 11171, 11177, 11711, 11717, 11771, 11777, 17111, 17117, 17171, 17177, 17711, 17717 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that product of digits of n is a power of 7.

LINKS

Table of n, a(n) for n=1..44.

EXAMPLE

7717 is in the sequence because 7*7*1*7 = 343 = 7^3.

MATHEMATICA

Select[Range[20000], IntegerQ[Log[7, Times@@(IntegerDigits[#])]] &] (* or *) Flatten[Table[FromDigits/@Tuples[{1, 7}, n], {n, 6}]]

PROG

(MAGMA) [n: n in [1..24000] | Set(Intseq(n)) subset {1, 7}];

(PARI) is(n) = my(d=digits(n), e=[0, 2, 3, 4, 5, 6, 8, 9]); if(#setintersect(Set(d), Set(e))==0, return(1), return(0)) \\ Felix Fröhlich, Aug 19 2016

CROSSREFS

Cf. similar sequences listed in A276037.

Cf. A002275, A002281, A034054.

Sequence in context: A094104 A167513 A260891 * A199327 A260892 A020455

Adjacent sequences:  A276036 A276037 A276038 * A276040 A276041 A276042

KEYWORD

nonn,base

AUTHOR

Vincenzo Librandi, Aug 19 2016

STATUS

approved

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Last modified May 19 13:08 EDT 2019. Contains 323393 sequences. (Running on oeis4.)