A078250 a(1) = 1, a(n) = smallest multiple of n using prime digits if n is composite else smallest multiple of n using composite digits, with a(n) = 0 if there are none.

1, 4, 6, 32, 40, 72, 49, 32, 27, 0, 44, 72, 468, 252, 75, 32, 68, 72, 494, 0, 252, 22, 46, 72, 25, 52, 27, 252, 406, 0, 496, 32, 33, 272, 35, 72, 444, 532, 273, 0, 984, 252, 86, 352, 225, 322, 94, 2352, 735, 0, 255, 52, 689, 2322, 55, 2352, 57, 232, 649, 0

Offset: 1

Author

Amarnath Murthy, Nov 24 2002

Keywords

• base
• easy
• nonn

Comments

Besides multiples of 10, 625 and its odd multiples have a(n)=0. Based on comment by Robert Israel in A078239. - Andrew Howroyd, Sep 17 2024

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A074162, A078239, A078240.

Programs

PARI

a(n)={if(n%10==0||n%1250==625, 0, if(n==1, 1, my(S=Set([2, 3, 5, 7])); forstep(m=n, oo, n, my(d=digits(m)); if(0 == #if(isprime(n),select(t->t==1||setsearch(S, t), d), select(t->!setsearch(S,t),d)), return(m)))))} \\ Andrew Howroyd, Sep 17 2024

Extensions

a(13) corrected and a(29) onwards from Andrew Howroyd, Sep 17 2024