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A297645
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Hexagonal numbers (A000384) in which parity of digits alternates.
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4
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1, 6, 45, 276, 325, 496, 561, 630, 703, 2145, 2701, 6903, 8385, 10585, 14365, 18721, 25878, 38503, 47278, 74305, 89676, 90525, 107416, 109278, 147696, 149878, 210925, 254541, 303810, 345696, 349030, 383250, 454581, 527878, 561270, 674541, 705078, 709836
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OFFSET
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1,2
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COMMENTS
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LINKS
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EXAMPLE
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6903 is in the sequence because 6, 9, 0 and 3 have even and odd parity alternately.
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MAPLE
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filter:= proc(n) local L;
if n < 10 then return true fi;
L:= convert(n, base, 10) mod 2;
not has(L[2..-1]-L[1..-2], 0)
end proc:
select(filter, [seq(n*(2*n-1), n=1..10^4)]); # Robert Israel, Jan 05 2018
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PROG
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(PARI)
is_alt(n) = m=n; e=n%10; n\=10; while(n>0, f=n%10; if(e%2==f%2, return, e=f; n\=10)); return(m)
select(is_alt, vector(1000, n, (4*n^2-2*n)/2))
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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