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A154545 Odd nonprimes k such that the smallest digit of k + the number of smallest digits of k is prime. 1

%I

%S 1,15,21,25,27,33,45,49,51,55,69,81,91,99,115,117,119,121,123,125,129,

%T 133,135,141,143,145,147,153,155,159,161,165,169,171,175,177,183,185,

%U 187,189,195,213,215,217,219,221,231,235,237,243,245,247,249,253,255

%N Odd nonprimes k such that the smallest digit of k + the number of smallest digits of k is prime.

%H Jinyuan Wang, <a href="/A154545/b154545.txt">Table of n, a(n) for n = 1..10000</a>

%e 1 is the smallest digit of 15 and it appears once, 1+1 is prime so 15 appears in the sequence; and so does 21, 51, 81, 91.

%p frequdig := proc(n,dig) local f,d ; f := 0 ; for d in convert(n,base,10) do if d = dig then f :=f+1; end if; end do; f ; end proc:

%p A054054 := proc(n) min(op(convert(n,base,10)) ) ; end proc:

%p for n from 1 to 500 by 2 do if not isprime(n) then sdg := A054054(n) ; a := sdg +frequdig(n,sdg) ; if isprime(a) then printf("%d,",n ) ; end if; end if; end do: # _R. J. Mathar_, May 05 2010

%Y Cf. A054054 (smallest digit of n).

%K nonn,base,less

%O 1,2

%A _Juri-Stepan Gerasimov_, Jan 11 2009

%E Entries checked by _R. J. Mathar_, May 05 2010

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Last modified August 17 19:38 EDT 2022. Contains 356189 sequences. (Running on oeis4.)