OFFSET
1,1
COMMENTS
Kaplan (2007) has shown that this is a subsequence of A117223 (and thus of A160350; see there for the reference), i.e., the cyclotomic polynomial phi(n) has coefficients in {0,1,-1} for indices n listed here.
This is a subsequence of A160352 which drops the requirement that p > 2.
See A160350 for further details and references.
LINKS
Robin Visser, Table of n, a(n) for n = 1..10000
EXAMPLE
a(1) = 435 = 3*5*29 is the smallest product of odd primes p < q < r such that r is congruent to +/- 1 modulo the product of the smaller factors, p*q.
PROG
(PARI) forstep( pqr=1, 9999, 2, my(f=factor(pqr)); #f~==3 & vecmax(f[, 2])==1 & abs((f[3, 1]+1)%(f[1, 1]*f[2, 1])-1)==1 & print1(pqr", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
M. F. Hasler, May 11 2009
STATUS
approved