A082128 - OEIS

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A082128

Smallest difference>1 between d and p/d for any divisor d of the partial product p of the sequence, starting with 21.

21, 4, 5, 13, 8, 2, 32, 16, 64, 512, 131072, 4194304, 8589934592, 9007199254740992, 75557863725914323419136, 20769187434139310514121985316880384

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OFFSET

0,1

COMMENTS

For n>3, the members are all powers of two. Proved by Luke Pebody, pers. comm.

LINKS

Table of n, a(n) for n=0..15.

PROG

(PARI) p=21; print1(p, ", "); for(n=1, 50, v=divisors(p); r=sqrt(p); t=0; for(k=1, matsize(v)[2], if(v[k]>=r, t=k; break)); if(v[t]^2==p, u=t, u=t-1); if(v[t]-v[u]<2, u=u-1; t=t+1); print1(v[t]-v[u]", "); p=p*(v[t]-v[u]))

CROSSREFS

Cf. A082120, A003681 (starts with 2, 3).

Sequence in context: A263277 A040428 A040429 * A034082 A040427 A070988

Adjacent sequences: A082125 A082126 A082127 * A082129 A082130 A082131

KEYWORD

nonn,hard

AUTHOR

Ralf Stephan, Apr 04 2003

STATUS

approved