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A068872 Composite numbers with all divisors congruent to 1 mod 10. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified February 21 07:18 EST 2018. Contains 299390 sequences. (Running on oeis4.)