OFFSET
1,2
COMMENTS
This sequence is motivated by the article by L. Panaitopol. Actually he defines q(n) = A000961(n-1), and Q(n) = q(n+1)-2*q(n)+q(n-1). Then he asks if the sequence of indices n such that Q(n)=0 is infinite.
LINKS
Laurentiu Panaitopol, Some of the properties of the sequence of powers of prime numbers, Rocky Mountain Journal of Mathematics, Volume 31, Number 4, Winter 2001.
EXAMPLE
In A000961, 7 is followed by 8 and 9, a 3-term arithmetic progression with a common difference 1.
9 is followed by 11 and 13, a 3-term arithmetic progression with a common difference 2.
PROG
(PARI) ispp(n) = isprimepower(n) || (n==1);
lista(nn) = {v = select(x->ispp(x), vector(nn, i, i)); for (k=2, #v-1, if (v[k+1] - 2*v[k] + v[k-1] == 0, print1(v[k-1], ", ")); ); }
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Nov 16 2014
STATUS
approved