OFFSET
1,1
COMMENTS
For the 132 terms (< 5*10^11) of the b-file for A019278, and using an extended list of terms, it can be checked that a(n) is not 0, even if the precise value is not known. For instance, a(51) <= 8097830664651.
Then a(52) to a(82) are: 4, 9, 1197, 8, 256, 4, 65155475, 64, 4096, 16, 195205791, 1387, 7, 37791, 4, 119, 8, 35136, 225, 64, 69127695, 2129920, 256, 4, 19671223, 9, 2, 1379763, 8, 90, 4096. And a(83) <= 7758260899200.
a(51) and a(83) are > 10^9.
EXAMPLE
With A019278 starting as 1, 2, 4, 8, 15, 16, 21, 24, 42, 60, 64, ...
one gets the proper multiples 2, 4, 8, 16, 60, 64, ...
and so the sequence begins: 2, 2, 2, 2, 4, 4, ...
PROG
(PARI) a(n, v019278) = my(m = v019278[n]); my(k=2, y = k*m); while (denominator(sigma(sigma(y))/y) != 1, k++; y += m); k;
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Michel Marcus, Jan 27 2020
STATUS
approved