OFFSET

1,2

COMMENTS

See A319522 for a similar sequence.

The function n -> (a(n), A319522(n)) establishes a bijection from N to N x N (where N = A000027); see A319523 for the corresponding inverse function.

This sequence has similarities with A059905: here we keep one p-adic valuation out of two, there we keep one binary digit out of two.

FORMULA

EXAMPLE

a(42) = a(prime(1)) * a(prime(2)) * a(prime(4)) = prime(1) * 1 * 1 = 2.

PROG

(PARI) a(n) = my (f=factor(n)); prod(i=1, #f~, my (pi=primepi(f[i, 1])); if (pi%2==1, prime(1+pi\2)^f[i, 2], 1))

CROSSREFS

KEYWORD

nonn,mult

AUTHOR

Rémy Sigrist, Sep 22 2018

STATUS

approved