A285011 Numbers with digits 7 and 9 only.

7, 9, 77, 79, 97, 99, 777, 779, 797, 799, 977, 979, 997, 999, 7777, 7779, 7797, 7799, 7977, 7979, 7997, 7999, 9777, 9779, 9797, 9799, 9977, 9979, 9997, 9999, 77777, 77779, 77797, 77799, 77977, 77979, 77997, 77999, 79777, 79779, 79797, 79799, 79977, 79979

Offset

1,1

Links

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

Mathematica

Flatten@ Table[FromDigits /@ Tuples[{7, 9}, n], {n, 5}] (* Giovanni Resta, Apr 10 2017 *)

Prog

(Magma) [n: n in [1..100000] | Set(IntegerToSequence(n, 10)) subset {7, 9}]
(PARI) a(n, {p=[7, 9]})={my(v=binary(n+1)); fromdigits(vector(#v-1, i, p[2]*v[i+1]+p[1]*!v[i+1]))} \\ R. J. Cano, Apr 09 2017
(Python)
def a(n): return int(bin(n+1)[3:].replace('0', '7').replace('1', '9'))
print([a(n) for n in range(1, 45)]) # Michael S. Branicky, Jul 09 2021

Crossrefs

Prime terms are in A020471.

Numbers with digits 7 and k only for k = 0 - 6 and 8 - 9: A204094 (k = 0), A276039 (k = 1), A284921 (k = 2), A143967 (k = 3), A284971 (k = 4), A284380 (k = 5), A256292 (k = 6), A256340 (k = 8), this sequence (k = 9).

Sequence in context: A087336 A178427 A106132 * A317401 A137058 A116237

Adjacent sequences: A285008 A285009 A285010 * A285012 A285013 A285014

Keyword

nonn,base

Author

Jaroslav Krizek, Apr 08 2017

Status

approved