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A202111
a(n) = sigma(n) - p, where p is the largest prime < sigma(n).
3
1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 5, 1, 1, 1, 2, 1, 2, 1, 1, 1, 5, 1, 1, 2, 1, 3, 3, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 3, 1, 1, 7, 1, 1, 5, 1, 1, 11, 4, 4, 1, 1, 1, 7, 1, 7, 1, 1, 1, 1, 1, 7, 1, 14, 1, 5, 1, 13, 7, 5, 1, 2, 1, 1, 11, 1, 7, 1, 1, 5, 8, 13, 1, 1, 1, 1, 7, 1, 1, 1, 3, 1, 1, 5, 7, 1, 1, 4, 5, 6, 1, 5, 1, 11, 1, 5
OFFSET
2,3
LINKS
FORMULA
a(n) = A049711(A000203(n)). - R. J. Mathar, Dec 13 2011
EXAMPLE
a(12) = sigma(12) - 23 = 28 - 23 = 5.
MAPLE
A202111 := proc(n)
A049711(numtheory[sigma](n) );
end proc:
seq(A202111(n), n=2..80) ; # R. J. Mathar, Dec 13 2011
MATHEMATICA
f[n_]:=Module[{nf=DivisorSigma[1, n]}, nf-NextPrime[nf, -1]]; f/@Range[3, 90]
PROG
(PARI)
A049711(n) = (n-precprime(n-1)); \\ This function from M. F. Hasler, Sep 09 2015
A202111(n) = A049711(sigma(n)); \\ Antti Karttunen, Nov 07 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Dec 11 2011
EXTENSIONS
More terms from Antti Karttunen, Nov 07 2017
STATUS
approved