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A176069
Numbers of the form k^2+k+1 that are the product of two distinct primes.
3
21, 57, 91, 111, 133, 183, 381, 553, 703, 813, 871, 993, 1057, 1191, 1261, 1333, 1561, 1641, 1807, 1893, 1981, 2071, 2257, 2353, 2653, 2757, 2863, 3193, 3661, 4033, 4291, 4971, 5257, 5403, 5853, 6807, 6973, 7141, 7311, 7483, 8373, 8557, 8743, 9121, 9313, 9507, 9703
OFFSET
1,1
LINKS
EXAMPLE
21 is a term as 21 = 3*7 = 4^2+4+1; 21 is the product of two distinct primes and 21 is of the form k^2 + k + 1.
MATHEMATICA
f[n_]:=Last/@FactorInteger[n]=={1, 1}; Select[Array[ #^2+#+1&, 6!, 2], f[ # ]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Name corrected by David A. Corneth, May 29 2023
STATUS
approved