A280745 Primes that end a block of terms in A280864.

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

These are the Type II primes in A280864. For Type I, see A396303.

It is not difficult to show (see A280864) that when a prime appears "naked" in A280864, it either begins a block, in which case the next term is 2*p, or it ends a block. In the latter case we conjecture that the previous term in A280864 is 2*p. This is true for the first 10^7 terms of A280864.

This entry was revised by N. J. A. Sloane, Jun 13 2026. The former definition was "Primes p such that A280864(k)=p for some k and A280864(k-1)=m*p for some m>1."

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

Cf. A280864, A280745.

Sequence in context: A271069 A023301 A023329 * A142896 A193700 A241631

Adjacent sequences: A280742 A280743 A280744 * A280746 A280747 A280748

Keyword

nonn

Author

N. J. A. Sloane, Jan 13 2017

Extensions

Entry revised by N. J. A. Sloane, Jun 13 2026, so as to match A396303.

Status

approved