

A000221


Take sum of squares of digits of previous term; start with 5.


14



5, 25, 29, 85, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145
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OFFSET

1,1


COMMENTS

As the orbit of 5 under A003132, this could as well start with index 0.  M. F. Hasler, Apr 27 2018


REFERENCES

R. Honsberger, Ingenuity in Mathematics, Random House, 1970, p. 83.


LINKS



FORMULA

Ultimately periodic with period 8.


MATHEMATICA

NestList[Plus @@ IntegerDigits[ # ]^2 &, 5, 50]
PadRight[{5, 25, 29, 85}, 120, {4, 16, 37, 58, 89, 145, 42, 20}] (* Harvey P. Dale, Jan 14 2022 *)


PROG

(PARI) A000221(n)=[20, 4, 16, 37, 58, 89, 145, 42, 5, 25, 29, 85][n%8+8^(n<5)] \\ M. F. Hasler, May 24 2009, edited Apr 27 2018
(Magma) [5, 25, 29, 85] cat &cat[[89, 145, 42, 20, 4, 16, 37, 58]: n in [0..17]]; // Vincenzo Librandi, Jan 29 2013
(Haskell)
a000221 n = a000221_list !! (n1)
a000221_list = iterate a003132 5


CROSSREFS

Cf. A003132 (the iterated map), A003621, A039943, A099645, A031176, A007770, A000216 (starting with 2), A000218 (starting with 3), A080709 (starting with 4), A008460 (starting with 6), A008462 (starting with 8), A008463 (starting with 9), A139566 (starting with 15), A122065 (starting with 74169).  M. F. Hasler, May 24 2009


KEYWORD

nonn,base,easy,nice


AUTHOR



STATUS

approved



