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A072918 a(n) = p(n) - sigma(n), where p(n) is the least prime greater than sigma(n). 0
1, 2, 1, 4, 1, 1, 3, 2, 4, 1, 1, 1, 3, 5, 5, 6, 1, 2, 3, 1, 5, 1, 5, 1, 6, 1, 1, 3, 1, 1, 5, 4, 5, 5, 5, 6, 3, 1, 3, 7, 1, 1, 3, 5, 1, 1, 5, 3, 2, 4, 1, 3, 5, 7, 1, 7, 3, 7, 1, 5, 5, 1, 3, 4, 5, 5, 3, 1, 1, 5, 1, 2, 5, 13, 3, 9, 1, 5, 3, 5, 6, 1, 5, 3, 1, 5, 7, 1, 7, 5, 1, 5, 3, 5, 7, 5, 3, 2, 1, 6 (list; graph; refs; listen; history; internal format)
OFFSET

1,2

EXAMPLE

phi(4) = 7 and the least prime > 7 is 11; hence a(4) = 11 - 7 = 4.

MATHEMATICA

ps[n_]:=Module[{sn=DivisorSigma[1, n]}, NextPrime[sn]-sn]; ps/@Range[100]  [From Harvey P. Dale, Feb. 2, 2011]

CROSSREFS

Sequence in context: A070668 A072341 A011130 * A162944 A140582 A062866

Adjacent sequences:  A072915 A072916 A072917 * A072919 A072920 A072921

KEYWORD

easy,nonn

AUTHOR

Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Aug 11 2002

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Last modified February 15 15:20 EST 2012. Contains 205823 sequences.