A046273 Largest prime substring in 7^n (0 if none).

0, 7, 0, 43, 401, 7, 7649, 823, 4801, 3607, 82475249, 7326743, 41287201, 89, 23072849, 7561, 232930569601, 2630513987207, 8413597910449, 398895185373143, 297612001, 558545864083, 2988049, 3400809163

Offset: 0

Author

Patrick De Geest, Jun 15 1998

Keywords

• nonn

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..200

Crossrefs

Cf. A046265.

Programs

Mathematica

lpss[n_]:=Module[{idn7=IntegerDigits[7^n]},Max[Select[Flatten[ Table[ FromDigits/@ Partition[idn7,i,1],{i,Length[idn7]}]],PrimeQ]]]; Array[ lpss,25,0]/.-\[Infinity]->0 (* Harvey P. Dale, Aug 17 2013 *)