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 A284971 Numbers with digits 4 and 7 only. 5
 4, 7, 44, 47, 74, 77, 444, 447, 474, 477, 744, 747, 774, 777, 4444, 4447, 4474, 4477, 4744, 4747, 4774, 4777, 7444, 7447, 7474, 7477, 7744, 7747, 7774, 7777, 44444, 44447, 44474, 44477, 44744, 44747, 44774, 44777, 47444, 47447, 47474, 47477, 47744, 47747 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS MATHEMATICA Flatten@ Table[FromDigits /@ Tuples[{4, 7}, n], {n, 5}] (* Giovanni Resta, Apr 08 2017 *) PROG (MAGMA) [n: n in [1..100000] | Set(IntegerToSequence(n, 10)) subset {4, 7}] (PARI) is(n) = my(x=Set([4, 7]), y=Set([0, 1, 2, 3, 5, 6, 8, 9])); if(#setintersect(Set(digits(n)), x) > 0 && #setintersect(Set(digits(n)), y)==0, return(1)); 0 \\ Felix FrÃ¶hlich, Apr 08 2017 (Python) def a(n):   b = bin(n+1)[3:]   return int("".join(b.replace("0", "4").replace("1", "7"))) print([a(n) for n in range(1, 45)]) # Michael S. Branicky, Apr 07 2021 CROSSREFS Prime terms are in A020465. Numbers with digits 4 and k only for k = 0 - 3 and 5 - 9: A169967 (k = 0), A032822 (k = 1), A284920 (k = 2), A032834 (k = 3), A256290 (k = 5), A284634 (k = 6), this sequence (k = 7), A284972 (k = 8), A284973 (k = 9). Sequence in context: A059213 A093102 A199404 * A139030 A115439 A348625 Adjacent sequences:  A284968 A284969 A284970 * A284972 A284973 A284974 KEYWORD nonn,base AUTHOR Jaroslav Krizek, Apr 07 2017 STATUS approved

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Last modified June 30 19:43 EDT 2022. Contains 354945 sequences. (Running on oeis4.)