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A020995 Numbers n such that the sum of the digits of Fibonacci(n) is n. 6
0, 1, 5, 10, 31, 35, 62, 72, 175, 180, 216, 251, 252, 360, 494, 504, 540, 946, 1188, 2222 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Since the number of digits in the n-th Fibonacci number ~ n*log_10(Golden Ratio), theoretically this sequence is infinite, but then the average density of those digits = ~ 0.208987. - Robert G. Wilson v

Robert Dawson of Saint Mary's University says it is likely that 2222 is the last term, as (assuming that the digits are equally distributed) the expected digit sum is ~ 0.9*n. - Stefan Steinerberger, Mar 12 2006

Bankoff's short paper lists the first seven terms. - T. D. Noe, Mar 19 2012

No more terms < 150000. - Manfred Scheucher, Aug 03 2015

REFERENCES

Alfred S. Posamentier & Ingmar Lehmann, The (Fabulous) Fibonacci Numbers, Prometheus Books, NY, 2007, page 209.

LINKS

Table of n, a(n) for n=1..20.

Leon Bankoff, A Fibonacci Curiosity, Fibonacci Quarterly 14, Feb. 1976, p. 17.

Pat Ballew, Fibonacci Digit Sums, Pat's Blog, Sunday, 5 August 2012.

Ron Knott, The Mathematical Magic of the Fibonacci Numbers: Digit Sums

Manfred Scheucher, Sage Script

David Terr, On the Sums of Digits of Fibonacci Numbers, Fibonacci Quarterly 34, Aug. 1996, pp. 349-355.

EXAMPLE

Fibonacci(10) = 55 and 5+5 = 10.

MATHEMATICA

Do[ If[ Apply[ Plus, IntegerDigits[ Fibonacci[n]]] == n, Print[n]], {n, 1, 10^5} ] (* Sven Simon *)

Do[ If[ Mod[ Fibonacci[n], 9] == Mod[n, 9], If[ Plus @@ IntegerDigits[ Fibonacci[n]] == n, Print[n]]], {n, 0, 10^6}] (* Robert G. Wilson v *)

Select[Range[0, 10^5], Plus @@ IntegerDigits[Fibonacci[ # ]] == # &] (* Ron Knott, Oct 30 2010 *)

PROG

(PARI) isok(n) = sumdigits(fibonacci(n)) == n; \\ Michel Marcus, Feb 18 2015

CROSSREFS

Cf. A000045, A067515, A004090.

Sequence in context: A056422 A032296 A052648 * A174467 A005201 A221304

Adjacent sequences:  A020992 A020993 A020994 * A020996 A020997 A020998

KEYWORD

nonn,base,more

AUTHOR

Sven Simon

STATUS

approved

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Last modified September 25 15:05 EDT 2018. Contains 315391 sequences. (Running on oeis4.)