A180405 Smallest integer not yet present in the sequence such that the sum of the first a(n) terms of the sequence is a prime.

2, 1, 4, 6, 3, 7, 8, 10, 11, 15, 12, 18, 14, 16, 22, 24, 19, 31, 28, 20, 23, 37, 36, 30, 26, 34, 29, 35, 42, 38, 40, 32, 39, 45, 52, 44, 54, 46, 56, 60, 43, 51, 50, 64, 84, 48, 49, 53, 68, 58, 62, 78, 70, 66, 57, 59, 82, 92, 90, 88, 63, 77, 72, 94, 67, 79, 76, 102, 71, 81, 96, 100

Offset: 1

Author

Paolo P. Lava, Sep 02 2010

Keywords

• easy
• nonn

Comments

From an idea of Eric Angelini with additional terms from D. S. McNeil.

The partial sums of the sequence are 2, 3, 7, 13, 16, 23, 31, 41, 52, ...

The sequence is self-descriptive and says that the 2nd, 1st, 4th, 6th, 3rd, 7th, etc, term in the partial sums, namely 3, 2, 13, 23, 7, 31 etc, are primes.

Links

• Neal Gersh Tolunsky, Table of n, a(n) for n = 1..10000
• Eric Angelini, The sum of the a(n) first digits of S is a prime
• Eric Angelini, The sum of the a(n) first digits of S is a prime [Cached copy, with permission]

Crossrefs

Cf. A054408, A171007 (digits version), A363379 (complement).

Extensions

Examples replaced with a comment by R. J. Mathar, Nov 18 2010