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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 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 FrÃ¶hlich, 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.)