A308610 Numbers k such that Sum_{j=1..k} composite(j)^composite(j) is prime, where composite(j) is the j-th composite number.

7, 194, 219

Offset

1,1

Comments

If it exists, a(4) > 25800.

Links

Table of n, a(n) for n=1..3.

Example

7 is a term because for the first 7 composites, 4^4 + 6^6 + 8^8 + 9^9 + 10^10 + 12^12 + 14^14 = 11120933330250889 is prime.

Mathematica

f[ n_Integer ] := Block[ {k = n + PrimePi[ n ] + 1}, While[ k - PrimePi[ k ] - 1 != n, k++ ]; k ]; s = 0; Do[ s = s + f[n]^f[n]; If[ PrimeQ[ s ], Print[ n ] ], {n, 1, 1000} ]

Crossrefs

Cf. A000040, A002808, A053782, A073826, A132637.

Sequence in context: A030257 A159826 A012849 * A277420 A220754 A135809

Adjacent sequences: A308607 A308608 A308609 * A308611 A308612 A308613

Keyword

nonn,more,bref

Author

Metin Sariyar, Aug 23 2019

Status

approved