A280745 Primes p such that A280864(k)=p for some k and A280864(k-1)=m*p for some m>1.

13, 139, 379, 397, 647, 661, 967, 983, 997, 1021, 1063, 1109, 1129, 1187, 1201, 1223, 1231, 1249, 1289, 1297, 1307, 1453, 1481, 1487, 1499, 1543, 1553, 1597, 1607, 1613, 1621, 1637, 1667, 1697, 1723, 1759, 1789, 1831, 1867, 1873, 1879, 1907, 1933, 2011, 2029, 2069, 2083, 2089, 2141, 2309

Offset: 1

Author

N. J. A. Sloane, Jan 13 2017

Keywords

• nonn

Comments

Conjecture: m is always 2.

The conjecture is true for n up to 10^7.

These primes are exceptional, because it appears that usually a prime p in A280864 is followed by 2p, whereas for these primes p is preceded by 2p.

Examples

			13 is a term because A280864(23)=13 and A280864(22)=26.
		

Links

• Lars Blomberg, Table of n, a(n) for n = 1..10000 (first 1683 terms from N. J. A. Sloane)

Crossrefs

Cf. A280864, A280745.