

A068174


Define an increasing sequence as follows. Start with an initial term, the seed (which need not have the property of the sequence); subsequent terms are obtained by inserting/placing at least one digit in the previous term to obtain the smallest number with the given property. Here the property is be a prime.


1



9, 19, 109, 1009, 10009, 100019, 1000159, 10001569, 100001569, 1000015069, 10000135069, 100001350649, 1000013500649, 10000130500649, 100001303500649, 1000013032500649, 10000103032500649, 100001030325003649, 1000010130325003649, 10000101303250036493
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OFFSET

1,1


LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..300


EXAMPLE

The primes obtained by inserting/placing a digit in a(2) = 19 are 109, 139, 149, 179, 199 etc. and a(3)= 109 is the smallest.


MATHEMATICA

f[n_] := Block[{b = PadLeft[ IntegerDigits[n], Floor[ Log[10, n] + 1]], k = 0}, While[ !PrimeQ[ FromDigits[ Insert[b, k, 2]]], k++ ]; FromDigits[ Insert[b, k, 2]]]; NestList[ f, 9, 18]


CROSSREFS

Cf. A068166, A068167, A068169, A068170, A068171, A068172, A068173.
Sequence in context: A000981 A060227 A171066 * A165247 A177130 A240120
Adjacent sequences: A068171 A068172 A068173 * A068175 A068176 A068177


KEYWORD

base,nonn


AUTHOR

Amarnath Murthy, Feb 25 2002


EXTENSIONS

Edited by N. J. A. Sloane and Robert G. Wilson v, May 08 2002
Corrected and extended by Robert Gerbicz, Sep 06 2002


STATUS

approved



