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A061228
a(1) = 2, a(n) = smallest number greater than n which is not coprime to n.
18
2, 4, 6, 6, 10, 8, 14, 10, 12, 12, 22, 14, 26, 16, 18, 18, 34, 20, 38, 22, 24, 24, 46, 26, 30, 28, 30, 30, 58, 32, 62, 34, 36, 36, 40, 38, 74, 40, 42, 42, 82, 44, 86, 46, 48, 48, 94, 50, 56, 52, 54, 54, 106, 56, 60, 58, 60, 60, 118, 62, 122, 64, 66, 66, 70, 68, 134, 70, 72, 72
OFFSET
1,1
LINKS
FORMULA
a(2m) = 2m+2, a(p)= 2p if p is a prime.
a(n)= n + the smallest divisor (more than 1) of n.
a(p^k) = p^k + p if p is prime. - Robert Israel, Oct 21 2015
EXAMPLE
a(9) = 12 as 10 and 11 are coprime to 9. a(11) = 22 as 11 is a prime.
MAPLE
for n from 1 to 150 do if n=1 then printf(`%d, `, 2); fi: for k from n+1 to 2*n do if igcd(n, k)>1 then printf(`%d, `, k); break; fi: od: od:
# alternative:
2, seq(t + min(numtheory:-factorset(t)), t = 2..1000); # Robert Israel, Oct 21 2015
MATHEMATICA
Table[n+First@(First/@FactorInteger[n]), {n, 200}] (* Vladimir Joseph Stephan Orlovsky, Apr 08 2011 *)
PROG
(Haskell)
a061228 n = n + a020639 n -- Reinhard Zumkeller, May 06 2015
CROSSREFS
Cf. A046666, A064413. Equals A020639(n) + n.
Sequence in context: A056942 A115947 A247653 * A070229 A248835 A053568
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Apr 23 2001
EXTENSIONS
More terms from James A. Sellers, Apr 24 2001
STATUS
approved