A089174 A nonsense sequence (not well-defined).

2, 3, 7, 11, 13, 17, 19, 23, 37, 41, 59, 73, 101, 137, 157, 239, 257, 271, 547, 2153, 2251, 4649, 7309, 9091, 19697, 21683, 94331, 333667, 928163, 3324301, 4403881, 7532639, 8983031, 10901027, 1111211111, 11195538763, 139381546141, 1102732004467

Offset: 1

Author

Roger L. Bagula, Dec 07 2003

Keywords

• nonn
• base
• fini
• less

Comments

Previous name was: Unique prime factors in A007907 extended to modulo 10 (past 20 elements).

This sequence is finite based on the data given. Since the Mathematica code is the main source of information for this sequence the data and code match for the given digits = 30 component. Increasing digits to, say, 50, increases the number of terms for be factored in A007907 and increases the number of terms to be ordered. This gives more values of this sequence. Since the data is established this removes any more terms from being added, which makes it a finite sequence. - G. C. Greubel, Aug 17 2023

Examples

			A007907 = {1, 11, 121, 1221, 12321, 123321, ...} which factor as {(1^1), (11^1), (11^2), (3^1, 11^1, 37^1), (3^2, 37^2), (3^1, 11^1, 37^1, 101^1), ...}. The list of the factors and their powers, flattened, begins as {1, 1, 11, 1, 11, 2, 3, 1, 11, 1, 37, 1, 3, 2, 37, 2, ...}. The list of ordered prime values begins as {2, 3, 7, 11, ...}.
		

Crossrefs

Cf. A007907.

Programs

Mathematica

digits=30;
f[m_]= Table[If[Floor[m/2]>=n, Mod[n, 10], Mod[m-n, 10]], {n,m}];
A007907= Table[Sum[f[m][[i]]*10^(i-1), {i,m}], {m, digits}];
c= Flatten[Table[FactorInteger[A007907[[n]]], {n, digits-1}]];
Rest@Union[Table[If[PrimeQ[c[[n]]], c[[n]], 1], {n, Dimensions[c][[1]]}]]

Extensions

Edited by G. C. Greubel, Aug 17 2023