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A280745
Primes p such that A280864(k)=p for some k and A280864(k-1)=m*p for some m>1.
3
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
1,1
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.
LINKS
Lars Blomberg, Table of n, a(n) for n = 1..10000 (first 1683 terms from N. J. A. Sloane)
EXAMPLE
13 is a term because A280864(23)=13 and A280864(22)=26.
CROSSREFS
Sequence in context: A271069 A023301 A023329 * A142896 A193700 A241631
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jan 13 2017
STATUS
approved