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A062664 Composite and every divisor (except 1) contains the digit 2. 2
254, 422, 482, 502, 526, 529, 542, 562, 842, 1042, 1642, 2042, 2246, 2258, 2402, 2426, 2434, 2446, 2458, 2462, 2474, 2498, 2518, 2554, 2558, 2566, 2578, 2582, 2594, 2642, 2654, 2846, 2854, 2858, 2921, 3242, 3254, 3442, 4022, 4126, 4162, 4222, 4226 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

If k is in the sequence, then all composite divisors of k are in the sequence. - Robert Israel, Jul 11 2019

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

254 has divisors 1, 2, 127 and 254, all of which except 1 contain the digit 2.

MAPLE

filter:= proc(n) local D;

  if isprime(n) then return false fi;

  andmap(con2, numtheory:-divisors(n) minus {1})

end proc:

con2:= proc(n) option remember; member(2, convert(n, base, 10)) end proc:

select(filter, [$4..10000]); # Robert Israel, Jul 11 2019

MATHEMATICA

fQ[n_, dgt_] := Union[ MemberQ[#, dgt] & /@ IntegerDigits@ Rest@ Divisors@ n][[1]]; Select[ Range[2, 4230], !PrimeQ[#] && fQ[#, 2] &] (* Robert G. Wilson v, Jun 11 2014 *)

PROG

(MAGMA) [m:m in [2..4300] | not IsPrime(m) and #[d:d in Divisors(m)|2 in Intseq(d)] eq #Divisors(m)-1]; // Marius A. Burtea, Jul 11 2019

CROSSREFS

Cf. A062649, A062668, A062670, A062672, A062674, A062676, A062678, A062680, A243819.

Sequence in context: A263380 A144855 A110827 * A258696 A158249 A255178

Adjacent sequences:  A062661 A062662 A062663 * A062665 A062666 A062667

KEYWORD

base,easy,nonn

AUTHOR

Erich Friedman, Jul 04 2001

EXTENSIONS

Offset changed by Robert Israel, Jul 11 2019

STATUS

approved

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Last modified September 15 14:38 EDT 2019. Contains 327078 sequences. (Running on oeis4.)