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A115026
Limiting value of n under iteration of "sum of the digits raised to the power of the number of digits of n" (A101337).
0
1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2, 5, 1, 370, 370, 370, 370, 370, 1, 4, 5, 8, 1, 4, 370, 370, 370, 1, 370, 9, 1, 1, 370, 370, 370, 370, 370, 370, 370, 370, 370, 4, 370, 1, 370, 370, 370, 370, 1, 370, 370, 370, 370, 370, 370, 370, 370, 370, 160, 370, 370, 370, 370, 370, 370
OFFSET
1,2
COMMENTS
Iterate A101337 starting at n until reaching a constant value (like 370) or a cycle (like 160, 217, 352, 160, ...). In the latter case, a(n) takes the smallest value in the cycle (e.g., a(59) = 160). Since k*9^k < 10^k for all k > 34, each number n is guaranteed to yield a smaller number a(n) if n > 10^34, so every number reaches a constant or a cycle under this sequence.
Conjecture: no term is greater than 370. - Harvey P. Dale, Jun 08 2022
EXAMPLE
a(89)=370 since:
89 (2 digits): 8^2 + 9^2 = 145,
145 (3 digits): 1^3 + 4^3 + 5^3 = 190,
190 (3 digits): 1^3 + 9^3 + 0^3 = 730,
730 (3 digits): 7^3 + 3^3 + 0^3 = 370,
370 (3 digits): 3^3 + 7^3 + 0^3 = 370, etc.
So a(89) = 370 since 370 is a fixed point of A101337.
MATHEMATICA
Table[Min[FindTransientRepeat[NestList[Total[IntegerDigits[#]^IntegerLength[#]]&, n, 20], 3][[2]]], {n, 70}] (* Harvey P. Dale, Jun 08 2022 *)
CROSSREFS
Cf. A101337.
Sequence in context: A355370 A326344 A340270 * A360075 A101337 A135208
KEYWORD
nonn,base
AUTHOR
Sergio Pimentel, Feb 24 2006
STATUS
approved