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A120317
Consecutive refactorable numbers a(n)-1, a(n) in which 7 the smallest prime divisor of a(n).
0
6080399213078595601, 106451203123324908289, 842122675409157900289, 205035001401532317649921, 690310240598397005456401, 1125500133125681400538801, 1241419580861102113344769
OFFSET
1,1
FORMULA
a(n) is the first integer of the form (7*k)^(7-1) such that both a(n) and a(n)-1 is refactorable and 7 is the smallest prime divisor of a(n).
MAPLE
with(numtheory); RFC7:=[]: p:=ithprime(4): P:=[seq(ithprime(i), i=1..3)]; for w to 1 do for k from 3 to 12^4 by 2 do if andmap(z -> k mod z <> 0, P) then m:=p*k; n:=m^(p-1); t:=tau(n); n1:=n-1; t1:=tau(n1); if (n mod t = 0) and (n1 mod t1 = 0) then RFC7:=[op(RFC7), n]; print(ifactor(n)); fi fi; od od;
CROSSREFS
KEYWORD
nonn
AUTHOR
Walter Kehowski, Jun 20 2006
STATUS
approved