A244442 - OEIS

A244442

a(n) is the smallest prime p such that all the n numbers dip(p), dip(dip(p)), ..., dip(dip(...(dip(p))...)) are primes. The function dip is defined in the comment lines.

2, 2, 2, 834007, 53918617, 53918617

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OFFSET

1,1

COMMENTS

dip(m) is the number that is obtained from m by changing each zero digit of m to 1 and each nonzero digit i of m to the i-th prime.

For example dip(103)=2.1.5=215 and dip(19)=2.23=223.

Since each positive integer starts with a nonzero digit, dip is well defined.

LINKS

Table of n, a(n) for n=1..6.

EXAMPLE

a(4)=834007 because the four numbers:

1. dip(834007)=19.5.7.1.1.17=19571117,

2. dip(dip(834007)),

3. dip(dip(dip(834007))),

4. dip(dip(dip(dip(834007))))

are all primes and 834007 is the smallest prime with this property.

CROSSREFS

Cf. A000040.

Sequence in context: A207820 A186069 A280842 * A338700 A246471 A289814

Adjacent sequences: A244439 A244440 A244441 * A244443 A244444 A244445

KEYWORD

nonn,base,more,hard

AUTHOR

Jahangeer Kholdi and Farideh Firoozbakht, Jul 07 2014

STATUS

approved