login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A094830 Start with x = n, repeatedly replace x with x + sum of squares of digits of x until you reach a prime; sequence gives number of steps. 5
1, 0, 0, 6, 0, 4, 0, 11, 5, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 5, 13, 9, 0, 4, 11, 12, 17, 3, 0, 8, 0, 8, 7, 1, 7, 3, 0, 5, 7, 4, 0, 3, 0, 3, 7, 8, 0, 2, 2, 2, 6, 3, 0, 10, 2, 3, 1, 3, 0, 3, 0, 2, 2, 18, 2, 11, 0, 2, 6, 9, 0, 10, 0, 1, 1, 2, 5, 1, 0, 16, 2, 8, 0, 3, 11, 6, 10, 2, 0, 4, 1, 15, 2, 1, 9, 2, 0, 7, 7, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

It is currently not known if this sequence is well defined, i.e. if for all n>=1 there exists an integer v such that a(n) = v. If the sequence is not well defined then the given programs are incorrect as they will get stuck in an infinite loop for some integers. - Peter Luschny, Oct 28 2016

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

a(4)=6 because 4 -> 20 -> 24 -> 44 -> 76 -> 161 -> 199, takes 6 steps to reach a prime.

MAPLE

f:= proc(n) local x, k;

x:= n;

for k from 0 do

  if isprime(x) then return k fi;

  x:= x + add(t^2, t = convert(x, base, 10))

od;

end proc:

map(f, [$1..100]); # Robert Israel, Oct 27 2016

MATHEMATICA

p[n_]:=Length[NestWhileList[#+Total[IntegerDigits[#]^2]&, n, !PrimeQ[ #]&]]-1; Array[p, 100] (* Harvey P. Dale, Dec 03 2011 *)

PROG

a(n) = my(k=0); while(!isprime(n), d=digits(n); n+=vecsum(vector(#d, i, d[i]^2)); k++) ; k \\ David A. Corneth, Oct 27 2016

CROSSREFS

Cf. A003132, A094877.

Sequence in context: A089841 A202542 A019766 * A196878 A209835 A298528

Adjacent sequences:  A094827 A094828 A094829 * A094831 A094832 A094833

KEYWORD

base,easy,nonn,look

AUTHOR

Jason Earls, Jun 13 2004

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 14 01:33 EST 2019. Contains 329978 sequences. (Running on oeis4.)