A112534 Number of digits in A110778(n).
1, 1, 1, 3, 3, 21, 7, 31, 5, 480, 1526, 294, 1615
Offset: 1
Examples
A110778(4) = 777 hence a(4) = 3.
Crossrefs
Programs
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Mathematica
id[n_]:=IntegerDigits[n]; f[x_,y_]:=FromDigits[Flatten[Append[{x},y]]]; a[x_,y_]:=NestWhile[f[id[#],y]&,f[id[x],y],!PrimeQ[#]&]; le[n_]:=Length[id[n]]; d[x_,y_]:=x-FromDigits[PadRight[id[y],le[x]]]; x=3; t={1}; Do[y=a[x,7]; AppendTo[t,le[d[y,x]]]; x=a[y,3]; AppendTo[t,le[d[x,y]]],{n,5}]; t (* Jayanta Basu, May 20 2013 *) -
Python
from sympy import isprime from itertools import count, islice def agen(): # generator of terms s = "" while True: for d in "37": for k in count(1): if isprime(int(s+d*k)): break yield k s += d*k print(list(islice(agen(), 10))) # Michael S. Branicky, Aug 23 2022
Extensions
Typo in example fixed by Sean A. Irvine, Mar 21 2010
a(11)-a(12) from Sean A. Irvine, Mar 22 2010
a(13) from Michael S. Branicky, Aug 23 2022
Comments