Search: a020467 -id:a020467
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A260827
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Primes that contain only the digits (0, 5, 7).
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+10
6
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5, 7, 557, 577, 757, 5077, 5507, 5557, 7057, 7507, 7577, 7757, 50077, 50707, 50777, 55057, 57077, 57557, 70507, 75557, 75577, 75707, 77557, 500057, 500777, 505777, 507077, 507557, 507757, 550007, 550577, 550757, 555077, 555557, 555707, 557057, 570077, 575077
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A284380
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Numbers n with digits 5 and 7 only.
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+10
6
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5, 7, 55, 57, 75, 77, 555, 557, 575, 577, 755, 757, 775, 777, 5555, 5557, 5575, 5577, 5755, 5757, 5775, 5777, 7555, 7557, 7575, 7577, 7755, 7757, 7775, 7777, 55555, 55557, 55575, 55577, 55755, 55757, 55775, 55777, 57555, 57557, 57575, 57577, 57755, 57757
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A260831
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Primes that contain only the digits (5, 7, 9).
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+10
4
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5, 7, 59, 79, 97, 557, 577, 599, 757, 797, 977, 997, 5557, 5779, 7559, 7577, 7757, 7759, 55579, 55799, 55997, 57557, 57559, 57977, 59557, 59779, 59797, 59957, 59999, 75557, 75577, 75797, 75979, 75997, 77557, 77797, 77977, 77999, 79559, 79579, 79757, 79777
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A260828
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Primes that contain only the digits (1, 5, 7).
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+10
3
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5, 7, 11, 17, 71, 151, 157, 557, 571, 577, 751, 757, 1117, 1151, 1171, 1511, 1571, 1777, 5171, 5557, 5711, 5717, 7151, 7177, 7517, 7577, 7717, 7757, 11117, 11171, 11177, 11551, 11717, 11777, 15511, 15551, 17117, 17551, 51151, 51157, 51511, 51517, 51551, 51577
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A036320
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Composite numbers whose prime factors contain no digits other than 5 and 7.
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+10
2
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25, 35, 49, 125, 175, 245, 343, 625, 875, 1225, 1715, 2401, 2785, 2885, 3125, 3785, 3899, 4039, 4375, 5299, 6125, 8575, 12005, 13925, 14425, 15625, 16807, 18925, 19495, 20195, 21875, 26495, 27293, 27785, 28273, 30625, 37093, 37885, 38785
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COMMENTS
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FORMULA
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Sum_{n>=1} 1/a(n) = Product_{p in A020467} (p/(p - 1)) - Sum_{p in A020467} 1/p - 1 = 0.1179595738... . - Amiram Eldar, May 22 2022
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CROSSREFS
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A260829
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Primes that contain only the digits (5, 6, 7).
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+10
2
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5, 7, 67, 557, 577, 677, 757, 5557, 5657, 6577, 7577, 7757, 55667, 56767, 57557, 57667, 65557, 65657, 65677, 65777, 67567, 67577, 67757, 67777, 75557, 75577, 75767, 76667, 76757, 76777, 77557, 555557, 555677, 555767, 557567, 565567, 565667, 566557, 566567
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A260830
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Primes that contain only the digits (5, 7, 8).
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+10
2
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5, 7, 557, 577, 587, 757, 787, 857, 877, 887, 5557, 5857, 7577, 7757, 7877, 8887, 55787, 57557, 57587, 57787, 58757, 58787, 75557, 75577, 75787, 77557, 77587, 78577, 78787, 78857, 78877, 78887, 85577, 87557, 87587, 87877, 87887, 555557, 555857, 557857, 558587
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A036946
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Smallest n-digit prime containing only the digits 5 and 7, or 0 if no such prime exists.
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+10
1
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5, 0, 557, 5557, 57557, 555557, 5555777, 55555777, 555557557, 5555555557, 55555555777, 555555575557, 5555555757757, 55555555575757, 555555555555557, 5555555555557577, 55555555555777777, 555555555557557757, 5555555555555557577, 55555555555575755777
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