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Search: id:A090315
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| A090315 |
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Least k such that k and digit reversal of k both have n divisors, or 0 if no such number exist. |
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+0
1
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| 1, 2, 4, 6, 14641, 44, 0, 24, 484, 272, 0, 294, 0, 291008, 44944, 264, 0, 252, 0, 2992, 0, 2532352, 0, 2508, 10004000600040001, 2977792, 1002001, 2112, 0, 63536, 0, 4224, 0, 44356665344, 0, 2772, 0, 2380651036672, 0, 42224, 0, 6336, 0, 2937856, 698896, 0
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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For a(7) one needs a number of the form p^6 whose digit reversal is q^6, p, q are primes. Hence a(7) perhaps is zero (not sure). Conjecture: There are infinitely many nonzero terms as well as zeros in this sequence.
Zeros are unproved. I have checked for a(21) up to 10^13, a(46) up to 10^14, a(33) up to 10^18, a(39) up to 10^20, a(35) up to 10^30 and the rest (7, 11, 13, 17, 19, 23, 29, 31, 37, 41 and 43) up to at least 10^48. - David Wasserman (wasserma(AT)spawar.navy.mil), Nov 01 2005
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EXAMPLE
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a(8) =24, tau(24) = tau(42) = 8.
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CROSSREFS
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Cf. A083753.
Sequence in context: A056012 A066719 A033319 this_sequence A083753 A111512 A111768
Adjacent sequences: A090312 A090313 A090314 this_sequence A090316 A090317 A090318
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KEYWORD
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base,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Dec 01 2003
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EXTENSIONS
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More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Nov 01 2005
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