A200065 Start with n, concatenate its trivial divisors, and repeat until a prime is reached. a(n) = 0 if no prime is ever reached.

0, 0, 13, 0, 0, 0, 17, 0, 19, 0, 1111111111111111111, 0, 113, 0, 0, 0, 1117, 0, 11119, 0, 111121, 0, 1123, 0, 0, 0, 127, 0, 1129, 0, 131, 0

Offset

1,3

Comments

a(33) has 715 digits and is too large to include.

a(A065502(n)) = 0. There are other integers for which a(n) = 0 (i.e., n = 221).

The number (10^270343 - 1)/9 appears 161046 times in this sequence.

All odd primes from A096497 are in the sequence.

Links

Arkadiusz Wesolowski, Table of n, a(n) for n = 1..1032

Example

17 -> {1, 17} = 117 (composite) -> {1, 117} = 1117 (prime), so a(17) = 1117.

Mathematica

lst = {}; Do[If[DivisorSigma[0, n] == 1 || Divisible[n, 5] || EvenQ[n], AppendTo[lst, 0], If[PrimeQ[n], n = 10^Length[IntegerDigits[n]] + n]; While[True, If[PrimeQ[n], Break[]]; n = FromDigits[Flatten[IntegerDigits[{1, n}]]]]; AppendTo[lst, n]], {n, 32}]; lst

Crossrefs

Cf. A004022, A096497.

Sequence in context: A127708 A094896 A277118 * A067155 A277255 A255288

Adjacent sequences: A200062 A200063 A200064 * A200066 A200067 A200068

Keyword

base,nonn

Author

Arkadiusz Wesolowski, Apr 18 2012

Status

approved