OFFSET
1,1
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..5000
EXAMPLE
21 = 3*7 is present because 3 in binary is "11" ("011" when extended with a leading zero) and 7 in binary is "111", and these differ only in the bit-position 2 (with indexing where the least significant bit is in the position 0).
33 = 3*11 is present because 3 in binary is "11" ("0011" when extended with two leading zeros) and 11 in binary is "1011", and these differ only in the bit-position 3.
PROG
(PARI)
A020639(n) = if(1==n, n, vecmin(factor(n)[, 1]));
i=0; n=0; while(i < 5000, n++; if(isA261077(n), i++; write("b261077.txt", i, " ", n)));
(Scheme, with Antti Karttunen's IntSeq-library)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Antti Karttunen, Sep 22 2015
STATUS
approved