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 A028915 Take next group of 3 primes, beginning at 7, map final digits to base 4 by 1->0, 3->1, 7->3, 9->2; convert back to decimal. 0
 49, 57, 35, 7, 24, 49, 38, 49, 57, 51, 40, 55, 24, 7, 33, 57, 32, 54, 12, 23, 7, 15, 38, 54, 27, 10, 1, 38, 49, 59, 9, 33, 15, 24, 61, 35, 30, 1, 54, 7, 16, 43, 25, 12, 39, 56, 7, 41, 57, 49, 60, 43, 13, 51, 19, 38, 1, 40, 6, 49, 54, 54, 5, 3, 17, 54, 14, 46, 24, 49 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS The index corresponds to the n-th triple of primes, thus offset is 2 since we discard the first prime triple (2,3,5). REFERENCES Hans Paul van den Haag used this coding in Scientific American, German Edition, 4/1996 P.23. LINKS EXAMPLE 7,11,13 -> 7,1,3 -> 3 * 4^2 + 0 * 4^1 + 1 * 4^0 = 49. 17,19,23 -> 7,9,3 -> 3 * 4^2 + 2 * 4^1 + 1 * 4^0 = 57. MATHEMATICA p3[c_]:=FromDigits[(Mod[c, 10])/.{1->0, 3->1, 7->3, 9->2}, 4]; p3/@ Partition[ Prime[ Range[4, 220]], 3] (* Harvey P. Dale, Dec 15 2014 *) PROG (PARI) cod(d) = if (d==1, 0, if (d==3, 1, if (d==7, 3, if (d==9, 2)))); a(n) = cod(prime(3*n-2) % 10)*4^2 + cod(prime(3*n-1) % 10)*4 + cod(prime(3*n) % 10); \\ Michel Marcus, Aug 16 2013 CROSSREFS Sequence in context: A140388 A044863 A162527 * A090063 A143164 A304950 Adjacent sequences:  A028912 A028913 A028914 * A028916 A028917 A028918 KEYWORD nonn,base AUTHOR Armand Turpel (armand_t(AT)geocities.com, armand(AT)vo.lu) EXTENSIONS Offset changed from 7 to 2 by Michel Marcus, Aug 16 2013 STATUS approved

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Last modified August 22 20:33 EDT 2019. Contains 326183 sequences. (Running on oeis4.)