A320879 Primes such that iteration of A062028 (n + its digit sum) yields 7 primes in a row.

286330897, 10858338851, 12869802851, 15845166851, 29837412851, 45480846799, 56676324799, 56676324863, 68105187851, 73915118861, 114737845853, 129282912851, 154648223809, 155738371853, 207036953861, 271077075851, 358515148853, 373169411809, 373169411861, 395705343799

Offset: 1

Author

Zak Seidov and M. F. Hasler, Nov 08 2018

Keywords

• nonn
• base

Comments

The first 15 terms are immediately calculated from A320878(1..200) using the formula.

Links

• Lars Blomberg, Table of n, a(n) for n = 1..445 (Terms < 10^14)
• Carlos Rivera, Puzzle 163. P+SOD(P)

Crossrefs

Cf. A047791, A048519, A062028 (n + digit sum of n).

Cf. A048523 .. A048527.

a(1) = A090009(8) = start of first chain of 8 primes under iteration of A062028.

Subsequence of A320878; A320880 is a subsequence.

Programs

PARI

is_A320879(n)=isprime(n=A062028(n))&& is_A320878(n) \\ If possible, use this to select terms from a sufficiently large precomputed array A320878:
A320879 = select( is_A320879, A320878) \\ or, in that case, the more efficient:
A320879 = select( p->setsearch(A320878, A062028(p)), A320878) \\ or: vecextract(A320878, select(i->A062028(A320878[i])==A320878[i+1], [1..#A320878-1]))

Formula

A320879 = { n in A320878 | A062028(n) in A320878 } = { n = A320878(k) | A062028(n) = A320878(k+1) }.

Extensions

a(16)-a(20) from Lars Blomberg, Feb 10 2019