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A139566 a(n) is the sum of squares of digits of a(n-1); a(1)=15. 13
15, 26, 40, 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, 42, 20, 4, 16, 37 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
Eventually periodic with period 8.
a(n) = A008463(n) for n > 4. - M. F. Hasler, May 24 2009
a(n) = a(n-8) for n > 11. - Colin Barker, Aug 24 2015
G.f.: x*(36*x^10 + 6*x^9 - 27*x^8 - 145*x^7 - 89*x^6 - 58*x^5 - 37*x^4 - 16*x^3 - 40*x^2 - 26*x - 15) / ((x-1)*(x+1)*(x^2+1)*(x^4+1)). - Colin Barker, Aug 24 2015
MATHEMATICA
a = {15}; Do[AppendTo[a, Plus @@ (IntegerDigits[a[[ -1]]]^2)], {70}]; a (* Stefan Steinerberger, Jun 14 2008 *)
NestList[Total[IntegerDigits[#]^2] &, 15, 70] (* or *) PadRight[ {15, 26, 40}, 70, {42, 20, 4, 16, 37, 58, 89, 145}](* Harvey P. Dale, Jan 28 2013 *)
PROG
From M. F. Hasler, May 24 2009: (Start)
(PARI) /* to check the given terms */
a=[/* paste the terms here */]; a==vector(#a, n, k=if(n>1, A003132(k), 15))
/* to check the following code, use: a==vector(99, n, A139566(n)) */
A139566(n)=[15, 26, 40, 16, 37, 58, 89, 145, 42, 20, 4][if(n>11, (n-4)%8+4, n)] \\ (End)
(PARI) Vec(x*(36*x^10+6*x^9-27*x^8-145*x^7-89*x^6-58*x^5-37*x^4-16*x^3 -40*x^2-26*x-15)/((x-1)*(x+1)*(x^2+1)*(x^4+1)) + O(x^70)) \\ Colin Barker, Aug 24 2015
CROSSREFS
Cf. A003132 (the iterated map), A003621, A039943, A099645, A031176, A007770, A000216 (starting with 2), A000218 (starting with 3), A080709 (starting with 4), A000221 (starting with 5), A008460 (starting with 6), A008462 (starting with 8), A008463 (starting with 9), A122065 (starting with 74169). - M. F. Hasler, May 24 2009
Sequence in context: A050700 A263108 A274182 * A097963 A063936 A240914
KEYWORD
base,nonn,easy
AUTHOR
Robert Gornall (rob(AT)khobbits.net), Jun 11 2008
EXTENSIONS
More terms from Stefan Steinerberger, Jun 14 2008
Terms checked, using the given PARI code, by M. F. Hasler, May 24 2009
Minor edits and starting value added in name by M. F. Hasler, Apr 27 2018
STATUS
approved

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Last modified June 17 15:57 EDT 2024. Contains 373463 sequences. (Running on oeis4.)