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A214584
Integers whose decimal representation has only digits in {4,5,7}.
2
4, 5, 7, 44, 45, 47, 54, 55, 57, 74, 75, 77, 444, 445, 447, 454, 455, 457, 474, 475, 477, 544, 545, 547, 554, 555, 557, 574, 575, 577, 744, 745, 747, 754, 755, 757, 774, 775, 777, 4444, 4445, 4447, 4454, 4455, 4457, 4474, 4475, 4477, 4544, 4545, 4547, 4554, 4555, 4557, 4574, 4575, 4577, 4744
OFFSET
1,1
COMMENTS
These could be called crooked numbers. Integers all of whose numerals are written (san serif) with at least one right or acute angle. The subsequence of crooked primes begins: 5, 7, 47, 457, 547, 557, 577, 757.
Exponential density 0.477... = log 3/log 10. - Charles R Greathouse IV, Jul 22 2012
CROSSREFS
Cf. A072960 (numbers using only the curved digits 0, 3, 6, 8 and 9).
Sequence in context: A123368 A292164 A178439 * A198131 A200387 A082468
KEYWORD
nonn,base,easy
AUTHOR
Jonathan Vos Post, Jul 21 2012
STATUS
approved