A175188 Composite numbers of the form k*10^k + 1.

201, 40001, 500001, 6000001, 70000001, 800000001, 100000000001, 1100000000001, 12000000000001, 130000000000001, 1400000000000001, 15000000000000001, 160000000000000001, 1700000000000000001, 18000000000000000001, 190000000000000000001, 2000000000000000000001

Offset

1,1

References

M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 844.

Links

Table of n, a(n) for n=1..17.

M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].

Example

For k=2, 2*10^2 + 1 = 201 = 3*67.
For k=4, 4*10^4 + 1 = 40001 = 13*17*181.

Maple

with(numtheory):for k from 1 to 100 do: n:=k*10^k +1:if type(n, prime) = false then print(n):else fi:od:

Mathematica

Select[Table[k*10^k+1, {k, 1, 20}], CompositeQ] (* Amiram Eldar, Aug 14 2023 *)

Crossrefs

Intersection of A002808 and A064748.

Subsequence of A005381.

Cf. A216347.

Sequence in context: A371057 A305724 A167070 * A227152 A210166 A216376

Adjacent sequences: A175185 A175186 A175187 * A175189 A175190 A175191

Keyword

nonn

Author

Michel Lagneau, Mar 01 2010

Extensions

a(16)-a(17) added and name corrected by Amiram Eldar, Aug 14 2023

Status

approved