OFFSET
1,2
COMMENTS
This sequence has similarities with A087019.
LINKS
FORMULA
a(n) = n iff n is a power of 2 (A000079).
a(prime(i)^k) = prime(2*i-1)^k for any i > 0 and k > 0.
EXAMPLE
For n = 40:
- 40 = 5 * 2^3, so:
(11 7 5 3 2)
1 0 3
x 1 0 3
-------
1 0 3
0 0 0
+ 1 0 1
-----------
1 0 1 0 3,
- hence a(40) = 11 * 5 * 2^3 = 440.
PROG
(PARI) a(n) = { my (r=1, pp=factor(n)[, 1]~); for (i=1, #pp, for (j=1, #pp, my (p=prime(primepi(pp[i])+primepi(pp[j])-1), v=valuation(r, p), w=min(valuation(n, pp[i]), valuation(n, pp[j]))); if (w>v, r*=p^(w-v)))); r }
CROSSREFS
KEYWORD
nonn
AUTHOR
Rémy Sigrist, Apr 03 2021
STATUS
approved