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 A027762 Denominator of Sum_{p prime, p-1 divides 2*n} 1/p. 8
 6, 30, 42, 30, 66, 2730, 6, 510, 798, 330, 138, 2730, 6, 870, 14322, 510, 6, 1919190, 6, 13530, 1806, 690, 282, 46410, 66, 1590, 798, 870, 354, 56786730, 6, 510, 64722, 30, 4686, 140100870, 6, 30, 3318, 230010, 498, 3404310, 6, 61410, 272118, 1410, 6, 4501770 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS From the von Staudt-Clausen theorem, denominator(B_2n) = product of primes p such that (p-1)|2n. Same as A002445. REFERENCES G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers, 5th ed., Oxford Univ. Press, 1979, Th. 118. H. Rademacher, Topics in Analytic Number Theory, Springer, 1973, Chap. 1. LINKS R. Mestrovic, On a Congruence Modulo n^3 Involving Two Consecutive Sums of Powers, Journal of Integer Sequences, Vol. 17 (2014), 14.8.4. FORMULA a(n) = A002445(n). [Joerg Arndt, May 06 2012] PROG (PARI) a(n)= {     my(s=0);     forprime (p=2, 2*n+1, if( (2*n)%(p-1)==0, s+=1/p ) );     return( denominator(s) ); } /* Joerg Arndt, May 06 2012 */ CROSSREFS Cf. A027761, A006954. Sequence in context: A334900 A136375 A138706 * A002445 A151711 A130512 Adjacent sequences:  A027759 A027760 A027761 * A027763 A027764 A027765 KEYWORD nonn,frac AUTHOR STATUS approved

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Last modified September 24 12:38 EDT 2021. Contains 347642 sequences. (Running on oeis4.)