A068872 Composite numbers with all divisors congruent to 1 mod 10.

121, 341, 451, 671, 781, 961, 1111, 1271, 1331, 1441, 1661, 1681, 1891, 1991, 2101, 2201, 2321, 2501, 2651, 2761, 2911, 2981, 3091, 3131, 3421, 3641, 3721, 3751, 4061, 4141, 4331, 4411, 4631, 4681, 4741, 4961, 5041, 5071, 5371, 5401, 5611, 5731, 5921

Offset

1,1

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

Mathematica

fQ[n_] := ! PrimeQ@ n && Union@ Mod[ First /@ FactorInteger@ n, 10] == {1}; Rest@ Select[ Range@ 5950, fQ] (* Robert G. Wilson v, Mar 04 2012 *)

Prog

(Haskell)
a068872 n = a068872_list !! (n-1)
a068872_list = filter
   (all (== 1) . map (`mod` 10) . a027750_row) a002808_list
-- Reinhard Zumkeller, Mar 08 2012
(PARI) is(n)=!isprime(n) && n>1 && vecmax(factor(n)[, 1]%10)==1 \\ Charles R Greathouse IV, Jun 19 2016

Crossrefs

Cf. A027750, A002808.

Sequence in context: A254978 A254971 A112075 * A203856 A216166 A208242

Adjacent sequences: A068869 A068870 A068871 * A068873 A068874 A068875

Keyword

nonn

Author

Amarnath Murthy, Mar 19 2002

Extensions

More terms from Sascha Kurz, Mar 23 2002

Status

approved