OFFSET

1,1

COMMENTS

It seems that a(n) tends to be quite large when n is an odd multiple of 15. We have a(15) = 56815934175, a(45) = 170447802525, a(75) = 284079670875, and a(105) > 10^12. - Giovanni Resta, Sep 15 2017

EXAMPLE

For the equation psi(k - 3) + psi(k + 3) = 2*psi(k), the smallest solution is k = 26565.

PROG

(PARI) a001615(n) = my(f=factor(n)); prod(i=1, #f~, f[i, 1]^f[i, 2] + f[i, 1]^(f[i, 2]-1));

a(n) = {my(k=n+1); while (a001615(k-n)+a001615(k+n) != 2*a001615(k), k++); k; } \\ after Charles R Greathouse IV at A001615

CROSSREFS

KEYWORD

nonn

AUTHOR

Altug Alkan, Sep 14 2017

EXTENSIONS

a(15)-a(52) from Giovanni Resta, Sep 15 2017

STATUS

approved