OFFSET
1,1
COMMENTS
a(13) > 1.45*10^11.
a(14) > 5*10^12, if it exists. - Giovanni Resta, Feb 29 2020
EXAMPLE
2 is a term since its binary representation is 10, its binary reversal is 01 = 1 which is equal to the sum of the proper divisors of 2.
1881 is a term since its binary representation is 11101011001, its binary reversal is 10011010111 which is equal to 1239, which is also the sum of the proper divisors of 1881: 1 + 3 + 9 + 11 + 19 + 33 + 57 + 99 + 171 + 209 + 627 = 1239.
MATHEMATICA
Select[Range[10^5], DivisorSigma[1, #] - # == IntegerReverse[#, 2] &]
PROG
(PARI) isok(k) = sigma(k) - k == fromdigits(Vecrev(binary(k)), 2); \\ Michel Marcus, Feb 29 2020
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Amiram Eldar, Feb 28 2020
EXTENSIONS
a(13) from Giovanni Resta, Feb 29 2020
STATUS
approved