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A276039 Numbers using only digits 1 and 7. 11
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. A020455, 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 August 15 10:12 EDT 2020. Contains 336492 sequences. (Running on oeis4.)