A141841 a(n) is the first term that can be reduced in n steps via repeated interpretation of a(n) as a base b+1 number where b is the largest digit of a(n), such that b is always 7 so that each interpretation is base 8. Terms already fully reduced (i.e., single digits) are excluded.

17, 57, 71, 107, 4647, 11047, 25447, 61547, 170153, 115751335, 671434647, 5001243627, 45206165753

Offset

1,1

Comments

It is sometimes possible to compute additional terms by taking the last term, treating it as base 10 and converting to base 8. This may create a term minimally interpretable as base 8 which can converted back to base 10 yielding the previous term in the sequence which will itself yield N further terms. But there is no guarantee (except in base 2) that the term so derived will be the first term to produce a sequence of N+1 terms. There could be another, smaller, term which satisfies that requirement but which uses different terms. Pushing the last term of this sequence produces the value 5001243627 which is minimally interpretable as base 8.

Links

Table of n, a(n) for n=1..13.

Example

a(3) = 71 because 71 is the first number that can produce a sequence of three terms by repeated interpretation as a base 8 number: [71] (base-8) --> [57] (base-8) --> [47] (base-8) --> [39]. Since 39 cannot be minimally interpreted as a base 8 number, the sequence terminates with 47. a(1) = 17 because 17 is the first number that can be reduced once, yielding no further terms minimally interpretable as base 8.

Crossrefs

Cf. A091049, A141836, A141837, A141838, A141839, A141840, A141842.

Sequence in context: A290763 A253417 A117390 * A146682 A146650 A147131

Adjacent sequences: A141838 A141839 A141840 * A141842 A141843 A141844

Keyword

base,more,nonn

Author

Chuck Seggelin (seqfan(AT)plastereddragon.com), Jul 10 2008

Extensions

a(12)-a(13) from Giovanni Resta, Feb 23 2013

Status

approved