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A173699 a(n+1) is the smallest integer > a(n) such that the concatenation of  [a(n+1)-a(n)] and a(n+1) is a prime number. 0
1, 3, 7, 9, 11, 17, 21, 23, 33, 47, 53, 57, 61, 63, 67, 69, 71, 77, 83, 87, 91, 93, 101, 111, 113, 131, 141, 143, 1007, 1011, 1013, 1017, 1019, 1023, 1031, 1047, 1051, 1057, 1059, 1061, 1083, 1127, 1131, 1141, 1143, 1157, 1161, 1163, 1169, 1181, 1199, 1203, 1229, 1233, 10027, 10039, 10051, 10053, 10097, 10131 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..60.

EXAMPLE

The second term is 3 because 23 is prime [concatenation of  the difference (3-1) and 3]. The third term is 7 because 47 is prime [concatenation of the difference (7-3) and 7]. The next term is 9 because 29 is prime [concatenation of the difference (9-7) and 9]. And so on. The next term is always the smallest available.

MAPLE

S2:= proc(n) option remember; local a, d;

       if n=1 then 1

     else a:= S2(n-1);

          for d while not isprime(parse(cat(d, a+d)))

          do od; a+d

       fi

     end:

seq(S2(n), n=1..60);

CROSSREFS

Sequence in context: A256465 A275386 A275602 * A287202 A156770 A088630

Adjacent sequences:  A173696 A173697 A173698 * A173700 A173701 A173702

KEYWORD

nonn,base

AUTHOR

Alois P. Heinz and Eric Angelini, Nov 25 2010

STATUS

approved

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Last modified June 6 13:49 EDT 2020. Contains 334827 sequences. (Running on oeis4.)