A028915 - OEIS

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.

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

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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

Table of n, a(n) for n=2..71.

Index entries for sequences related to final digits of numbers

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 * A345114 A090063 A143164

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