The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A199745 Numbers such that the sum of the largest and the smallest prime divisor equals the sum of the other distinct prime divisors. 4
 2145, 2730, 4641, 4845, 5005, 5460, 5610, 6435, 7410, 8190, 8778, 9177, 10725, 10920, 11220, 11305, 11730, 13485, 13585, 13650, 13923, 14535, 14820, 16380, 16830, 17017, 17556, 19110, 19305, 20010, 20930, 21489, 21505, 21840, 22230, 22440, 23460, 23529, 23595 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The definition implies that members of the sequence have at least four distinct prime factors. An even term must have at least five distinct prime factors. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..1000 FORMULA n such that A008472(n)/2 = A074320(n) = A020639(n) + A006530 (n). - Ray Chandler, Nov 10 2011 Sum_{k=2..A001221(a(n))} A027748(a(n),k) = A027748(a(n),1) + A027748(a(n), A001221(a(n))). - Reinhard Zumkeller, Nov 10 2011 EXAMPLE 22440 is in the sequence because the distinct prime divisors are {2, 3, 5, 11, 17} and 17+2 = 3+5+11. MAPLE isA199745 := proc(n) local p; p := sort(convert(numtheory[factorset](n), list)) ; if nops(p) >= 3 then return ( op(1, p) + op(-1, p) = add(op(i, p), i=2..nops(p)-1) ) ; else false; end if; end proc: for n from 2 to 20000 do if isA199745(n) then printf("%d, ", n) ; end if ; end do: # R. J. Mathar, Nov 10 2011 MATHEMATICA Select[Range[25000], Plus@@(pl=First/@FactorInteger[#])/2==pl[[1]]+pl[[-1]]&] (* Ray Chandler, Nov 10 2011 *) PROG (Sage) def isA199745(n) : p = factor(n) return len(p) > 2 and p[0][0] + p[-1][0] == add(p[i][0] for i in (1..len(p)-2)) [n for n in (2..20000) if isA199745(n)] # Peter Luschny, Nov 10 2011 (Haskell) a199745 n = a199745_list !! (n-1) a199745_list = filter (\x -> 2 * (a074320 x) == a008472 x) [1..] -- Reinhard Zumkeller, Nov 10 2011 CROSSREFS Cf. A020639, A006530, A074320, A008472, A109353. Sequence in context: A347040 A252547 A211601 * A200145 A179271 A118576 Adjacent sequences: A199742 A199743 A199744 * A199746 A199747 A199748 KEYWORD nonn AUTHOR Michel Lagneau, Nov 09 2011 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified March 31 19:18 EDT 2023. Contains 361672 sequences. (Running on oeis4.)