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Search: id:A127312
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| A127312 |
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Numbers n such that the sum of the digits of n and of n+1 is prime and 2n + 1 is also prime. |
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| 1, 2, 3, 5, 6, 8, 11, 14, 15, 18, 20, 21, 23, 26, 30, 33, 35, 36, 41, 44, 50, 51, 53, 54, 56, 63, 65, 68, 74, 78, 81, 83, 86, 90, 95, 96, 99, 105, 111, 113, 114, 116, 120, 125, 128, 131, 134, 135, 140, 141, 146, 153, 155, 158, 168, 173, 176, 186, 191, 194, 198, 200
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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Sum of the digits of 21 and 22 is 2+1+2+2 = 7 and 21+22 = 43. Both 7 and 43 are prime, hence 21 is a term.
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MAPLE
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sod:=proc(n) local b: b:=n->convert(n, base, 10): sum(b(n)[j], j=1..nops(b(n))) end: a:=proc(n) if isprime(2*n+1)=true and isprime(sod(n)+sod(n+1))=true then n else fi end: seq(a(n), n=1..280); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 01 2007
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PROGRAM
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(MAGMA) [ n: n in [1..200] | IsPrime(&+Intseq(n, 10) + &+Intseq(n+1, 10)) and IsPrime(2*n+1) ]; /* Klaus Brockhaus, Apr 06 2007 */
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CROSSREFS
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Sequence in context: A105760 A050834 A095172 this_sequence A081830 A117517 A098491
Adjacent sequences: A127309 A127310 A127311 this_sequence A127313 A127314 A127315
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KEYWORD
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nonn,base
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AUTHOR
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J. M. Bergot (thekingfishb(AT)yahoo.ca), Mar 28 2007
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EXTENSIONS
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Edited and extended by Emeric Deutsch (deutsch(AT)duke.poly.edu) and Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Apr 01 2007
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