OFFSET
1,1
COMMENTS
For every k > 1, the sequence includes 4^k - 2^(k+1), with m = 2^k - 2. - David Wasserman, Jan 29 2004
a(12) <= 16769024. a(13) <= 67092480. a(14) <= 268402688. a(15) <= 1073676288. [Donovan Johnson, Dec 19 2008]
PROG
(PARI) rad(n) = factorback(factorint(n)[, 1]); \\ A007947
isok(m) = {my(rm = rad(m), sm = rad(m+1)); for (k=1, m-1, if ((rad(k) == rm) && (rad(k+1) == sm), return (1)); ); } \\ Michel Marcus, Apr 05 2021
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Naohiro Nomoto, Oct 26 2003
EXTENSIONS
a(7)-a(11) from Donovan Johnson, Dec 19 2008
Name edited by Michel Marcus, Apr 06 2021
Confirmed a(12)-a(15) and extended with a(16) by Martin Ehrenstein, Apr 18 2021
STATUS
approved