reviewed

approved

proposed

reviewed

editing

proposed

allocated for Michel LagneauSmallest number k such that the difference between the greatest prime divisor and the smallest prime divisor of k equals n, or 0 if there is no such k.

2, 6, 15, 10, 21, 14, 55, 0, 33, 22, 39, 26, 85, 0, 51, 34, 57, 38, 115, 0, 69, 46, 203, 0, 145, 0, 87, 58, 93, 62, 259, 0, 185, 0, 111, 74, 205, 0, 123, 82, 129, 86, 235, 0, 141, 94, 371, 0, 265, 0, 159, 106, 413, 0, 295, 0, 177, 118, 183, 122, 469, 0, 335, 0

0,1

a(A007921(n)) = 0 where A007921(n) are the numbers that are not the difference of two primes.

a(2) = 15 because 15 = 3*5 and 5 - 3 = 2.

with(numtheory):for n from 0 to 65 do:ii:=0:for k from 2 to 10000 while(ii=0) do:x:=factorset(k):n1:=nops(x):d:=x[n1] - x[1]:if d=n then ii:=1: printf("%a, ", k):else fi:od:if ii=0 then printf("%a, ", 0):else fi:od:

Cf. A007921.

allocated

nonn

Michel Lagneau, Aug 02 2012

approved

editing

allocated for Michel Lagneau

allocated

approved